Apparatus and method incorporating an ultrasound transducer onto a delivery member

ABSTRACT

A medical device assembly and method provides an ultrasound transducer mounted onto a catheter shaft. The ultrasound transducer is mounted such that there is a radial separation between the transducer and the underlying catheter shaft. The transducer is mounted on support structures which do not bridge the gap between the transducer and delivery member. The location of the support structures provides for an “airbacked” transducer that is very efficient and prevents heat build-up in the materials in contact therewith.

RELATED APPLICATIONS

[0001] The present application claims priority under 35 U.S.C. §119(e)to U.S. Provisional Application No. 60/204,912, filed May 16, 2000.

TECHNICAL FIELD

[0002] The present invention is a surgical device and method. Morespecifically, it is a surgical device and method which provides anultrasound transducer assembly mounted on a catheter shaft forultrasonically coupling to a region of tissue in a body of a patient,and still more specifically for ultrasonically coupling to acircumferential region of tissue at a location where a pulmonary veinextends from an atrium.

BACKGROUND OF THE INVENTION

[0003] The terms “body space,” including derivatives thereof, is hereinintended to mean any cavity or lumen within the body which is defined atleast in part by a tissue wall. For example, the cardiac chambers, theuterus, the regions of the gastrointestinal tract, and the arterial orvenous vessels are all considered illustrative examples of body spaceswithin the intended meaning.

[0004] The term “body lumen,” including derivatives thereof, is hereinintended to mean any body space which is circumscribed along a length bya tubular tissue wall and which terminates at each of two ends in atleast one opening that communicates externally of the body space. Forexample, the large and small intestines, the vas deferens, the trachea,and the fallopian tubes are all illustrative examples of lumens withinthe intended meaning. Blood vessels are also herein considered lumens,including regions of the vascular tree between their branch points. Moreparticularly, the pulmonary veins are lumens within the intendedmeaning, including the region of the pulmonary veins between thebranched portions of their ostia along a left ventricle wall, althoughthe wall tissue defining the ostia typically presents uniquely taperedlumenal shapes.

[0005] Many local energy delivery devices and methods have beendeveloped for treating the various abnormal tissue conditions in thebody, and particularly for treating abnormal tissue along the body spacewalls which define the various body spaces in the body. For example,various devices have been disclosed with the primary purpose of treatingor recanalizing atherosclerotic vessels with localized energy delivery.Several disclosed devices and methods combine energy delivery assembliesin combination with cardiovascular stent devices in order to locallydeliver energy to tissue in order to maintain patency in diseased lumenssuch as blood vessels. Endometriosis, another abnormal wall tissuecondition which is associated with the endometrial cavity of the femaleand is characterized by dangerously proliferative uterine wall tissuealong the surface of the endometrial cavity, has also been treated bylocal energy delivery devices and methods. Several other devices andmethods have also been disclosed which use catheter-based heat sourcesfor the intended purpose of inducing thrombosis and controllinghemorrhaging within certain body lumens such as vessels.

[0006] Further, more detailed examples of local energy delivery devicesand related procedures such as those of the types just described aboveare variously disclosed in the following references: U.S. Pat. No.4,672,962 to Hershenson; U.S. Pat. No. 4,676,258 to InoKuchi et al.;U.S. Pat. No. 4,790,311 to Ruiz; U.S. Pat. No. 4,807,620 to Strul etal.; U.S. Pat. No. 4,998,933 to Eggers et al.; U.S. Pat. No. 5,035,694to Kasprzyk et al.; U.S. Pat. No. 5,190,540 to Lee; U.S. Pat. No.5,226,430 to Spears et al.; and U.S. Pat. No. 5,292,321 to Lee; U.S.Pat. No. 5,449,380 to Chin; U.S. Pat. No. 5,505,730 to Edwards; U.S.Pat. No. 5,558,672 to Edwards et al.; and U.S. Pat. No. 5,562,720 toStern et al. ; U.S. Pat. No. 4,449,528 to Auth et al.; U.S. Pat. No.4,522,205 to Taylor et al.; and U.S. Pat. No. 4,662,368 to Hussein etal.; U.S. Pat. No. 5,078,736 to Behl; and U.S. Pat. No. 5,178,618 toKandarpa.

[0007] Other previously disclosed devices and methods electricallycouple fluid to an ablation element during local energy delivery fortreatment of abnormal tissues. Some such devices couple the fluid to theablation element for the primary purpose of controlling the temperatureof the element during the energy delivery. Other such devices couple thefluid more directly to the tissue-device interface either as anothertemperature control mechanism or in certain other known applications asan actual carrier for the localized energy delivery, itself.

[0008] More detailed examples of ablation devices which use fluid toassist in electrically coupling electrodes to tissue are disclosed inthe following references: U.S. Pat. No. 5,348,554 to Imran et al.; U.S.Pat. No. 5,423,811 to Imran et al.; U.S. Pat. No. 5,505,730 to Edwards;U.S. Pat. No. 5,545,161 to Imran et al.; U.S. Pat. No. 5,558,672 toEdwards et al.; U.S. Pat. No. 5,569,241 to Edwards; U.S. Pat. No.5,575,788 to Baker et al.; U.S. Pat. No. 5,658,278 to Imran et al.; U.S.Pat. No. 5,688,267 to Panescu et al.; U.S. Pat. No. 5,697,927 to Imranet al.; U.S. Pat. No. 5,722,403 to McGee et al.; U.S. Pat. No.5,769,846; and PCT Patent Application Publication No. WO 97/32525 toPomeranz et al.; and PCT Patent Application Publication No. WO 98/02201to Pomeranz et al.

[0009] Cardiac Arrhythmias

[0010] Cardiac arrhythmias, and atrial fibrillation in particular,persist as common and dangerous medical ailments and are particularlyprevalent among the aging population. A patient with cardiac arrhythmiahas abnormal regions of cardiac tissue that do not follow thesynchronous beating cycle associated with normally conductive tissue.Instead, the abnormal regions of cardiac tissue conduct aberrant signalsto adjacent tissue, thereby disrupting the cardiac cycle and producingan asynchronous cardiac rhythm. Such abnormal conduction has beenpreviously known to occur at various regions of the heart, such as, forexample, in the region of the sino-atrial (SA) node, along theconduction pathways of the atrioventricular (AV) node and the Bundle ofHis, or in the cardiac muscle tissue forming the walls of theventricular and atrial cardiac chambers.

[0011] Cardiac arrhythmias, including atrial arrhythmia, may be of amultiwavelet reentrant type, characterized by multiple asynchronousloops of electrical impulses that are scattered about the atrial chamberand are often self-propagating. In the alternative or in addition to themultiwavelet reentrant type, cardiac arrhythmias may also have a focalorigin, such as when an isolated region of tissue in an atrium firesautonomously in a rapid, repetitive fashion. Cardiac arrhythmias,including atrial fibrillation, may be generally detected using theglobal technique of an electrocardiogram (EKG). More sensitiveprocedures of mapping the specific conduction along the cardiac chambershave also been disclosed, such as, for example, in U.S. Pat. No.4,641,649 to Walinsky et al. and Published PCT Patent Application No. WO96/32897 to Desai.

[0012] A host of clinical conditions may result from the irregularcardiac function and resulting hemodynamic abnormalities associated withatrial fibrillation, including stroke, heart failure, and otherthromboembolic events. In fact, atrial fibrillation is believed to be asignificant cause of cerebral stroke, wherein the abnormal hemodynamicsin the left atrium caused by the fibrillatory wall motion precipitatethe formation of thrombus within the atrial chamber. A thromboembolismis ultimately dislodged into the left ventricle which thereafter pumpsthe embolism into the cerebral circulation where a stroke results.Accordingly, numerous procedures for treating atrial arrhythmias havebeen developed, including pharmacological, surgical, and catheterablation procedures.

[0013] Several pharmacological approaches intended to remedy orotherwise treat atrial arrhythmias have been disclosed, such as forexample according to the disclosures of the following references: U.S.Pat. No. 4,673,563 to Berne et al.; U.S. Pat. No. 4,569,801 to Molloy etal.; and also “Current Management of Arrhythmias” (1991) by Hindricks,et al. However, such pharmacological solutions are not generallybelieved to be entirely effective in many cases, and are even believedin some cases to result in proarrhythmia and long term inefficacy.

[0014] Several surgical approaches have also been developed with theintention of treating atrial fibrillation. One particular example isknown as the “maze procedure,” as is disclosed by Cox, J L et al. in“The surgical treatment of atrial fibrillation. I. Summary” Thoracic andCardiovascular Surgery 101(3), pp. 402-405 (1991); and also by Cox, J Lin “The surgical treatment of atrial fibrillation. IV. SurgicalTechnique”, Thoracic and Cardiovascular Surgery 101(4), pp. 584-592(1991). In general, the “maze” procedure is designed to relieve atrialarrhythmia by restoring effective atrial systole and sinus node controlthrough a prescribed pattern of incisions about the tissue wall. In theearly clinical experiences reported, the “maze” procedure includedsurgical incisions in both the right and the left atrial chambers.However, more recent reports predict that the surgical “maze” proceduremay be substantially efficacious when performed only in the left atrium,such as is disclosed in Sueda et al., “Simple Left Atrial Procedure forChronic Atrial Fibrillation Associated With Mitral Valve Disease”(1996).

[0015] The “maze procedure” as performed in the left atrium generallyincludes forming vertical incisions from the two superior pulmonaryveins and terminating in the region of the mitral valve annulus,traversing the region of the inferior pulmonary veins en route. Anadditional horizontal line also connects the superior ends of the twovertical incisions. Thus, the atrial wall region bordered by thepulmonary vein ostia is isolated from the other atrial tissue. In thisprocess, the mechanical sectioning of atrial tissue eliminates thearrhythmogenic conduction from the boxed region of the pulmonary veinsand to the rest of the atrium by creating conduction blocks within theaberrant electrical conduction pathways. Other variations ormodifications of this specific pattern just described have also beendisclosed, all sharing the primary purpose of isolating known orsuspected regions of arrhythmogenic origin or propagation along theatrial wall.

[0016] While the “maze” procedure and its variations as reported by Coxand others have met some success in treating patients with atrialarrhythmia, its highly invasive methodology is believed to beprohibitive in most cases. However, these procedures have provided aguiding principle that electrically isolating faulty cardiac tissue maysuccessfully prevent atrial arrhythmia, and particularly atrialfibrillation caused by arrhythmogenic conduction arising from the regionof the pulmonary veins.

[0017] Less invasive catheter-based approaches to treat atrialfibrillation have been disclosed which implement cardiac tissue ablationfor terminating arrhythmogenic conduction in the atria. Examples of suchcatheter-based devices and treatment methods have generally targetedatrial segmentation with ablation catheter devices and methods adaptedto form linear or curvilinear lesions in the wall tissue which definesthe atrial chambers. Some specifically disclosed approaches provideablation elements that are linear over a defined length and are intendedto engage the tissue for creating the linear lesion. Other disclosedapproaches provide shaped or steerable guiding sheaths, or sheathswithin sheaths, for the intended purpose of directing tip ablationcatheters toward the posterior left atrial wall such that sequentialablations along the predetermined path of tissue may create the desiredlesion. In addition, various energy delivery modalities have beendisclosed for forming atrial wall lesions, and include use of microwave,laser, ultrasound, thermal conduction, and more commonly, radiofrequencyenergies to create conduction blocks along the cardiac tissue wall.

[0018] Further more detailed examples of ablation device assemblies andmethods for creating lesions along an atrial wall are disclosed in thefollowing U.S. patent references: U.S. Pat. No. 4,898,591 to Jang etal.; U.S. Pat. No. 5,104,393 to Isner et al.; U.S. Pat. No. 5,427,119;U.S. Pat. No. 5,487,385 to Avitall; U.S. Pat. No. 5,497,119 to Swartz etal.; U.S. Pat. No. 5,545,193 to Fleischman et al.; U.S. Pat. No.5,549,661 to Kordis et al.; U.S. Pat. No. 5,575,810 to Swanson et al.;U.S. Pat. No. 5,564,440 to Swartz et al.; U.S. Pat. No. 5,592,609 toSwanson et al.; U.S. Pat. No. 5,575,766 to Swartz et al.; U.S. Pat. No.5,582,609 to Swanson; U.S. Pat. No. 5,617,854 to Munsif; U.S. Pat. No.5,687,723 to Avitall; U.S. Pat. No. 5,702,438 to Avitall.

[0019] Other examples of such ablation devices and methods are disclosedin the following Published PCT Patent Applications: WO 93/20767 to Stemet al.; WO 94/21165 to Kordis et al.; WO 96/10961 to Fleischman et al.;WO 96/26675 to Klein et al.; and WO 97/37607 to Schaer.

[0020] Additional examples of such ablation devices and methods aredisclosed in the following published articles: “Physics and Engineeringof Transcatheter Tissue Ablation”, Avitall et al., Journal of AmericanCollege of Cardiology, Volume 22, No. 3:921-932 (1993); and “Right andLeft Atrial Radiofrequency Catheter Therapy of Paroxysmal AtrialFibrillation,” Haissaguerre, et al., Journal of CardiovascularElectrophysiology 7(12), pp. 1132-1144 (1996).

[0021] In addition to the known assemblies summarized above, additionaltissue ablation device assemblies have also been recently developed forthe specific purpose of ensuring firm contact and consistent positioningof a linear ablation element along a length of tissue. These assembliesanchor the element at one or more predetermined locations along thelength of tissue, such as in order to form a “maze”-type lesion patternin the left atrium. One example assembly includes an anchor at each oftwo ends of a linear ablation element. The anchors are used to securethe ends to each of two predetermined locations along a left atrialwall, such as at two adjacent pulmonary veins, so that tissue may beablated along the length of tissue extending therebetween.

[0022] In addition to attempting atrial wall segmentation with longlinear lesions for treating atrial arrhythmia, other ablation devicesand methods have also been disclosed which are intended to useexpandable members such as balloons to ablate cardiac tissue. Some suchdevices have been disclosed primarily for use in ablating tissue wallregions along the cardiac chambers. Other devices and methods have beendisclosed for treating abnormal conduction of the left-sided accessorypathways, and in particular associated with “Wolff-Parkinson-White”syndrome—various such disclosures use a balloon for ablating from withina region of an associated coronary sinus adjacent to the desired cardiactissue to ablate. Further more detailed examples of devices and methodssuch as of the types just described are variously disclosed in thefollowing published references: Fram et al., in “Feasibility of RFPowered Thermal Balloon Ablation of Atrioventricular Bypass Tracts viathe Coronary Sinus: In vivo Canine Studies,” PACE, Vol. 18, p 1518-1530(1995); “Long-term effects of percutaneous laser balloon ablation fromthe canine coronary sinus”, Schuger C D et al., Circulation (1992)86:947-954; and “Percutaneous laser balloon coagulation of accessorypathways”, McMath L P et al., Diagn Ther Cardiovasc Interven 1991;1425:165-171.

[0023] Cardiac Arrhythmias Originating from Foci in Pulmonary Veins

[0024] As discussed above, some modes of atrial fibrillation are focalin nature, caused by the rapid and repetitive firing of an isolatedcenter within cardiac muscle tissue associated with the atrium. Suchfoci may act as either a trigger of atrial fibrillatory paroxysmal ormay even sustain the fibrillation. Various disclosures have suggestedthat focal atrial arrhythmia often originates from at least one tissueregion along one or more of the pulmonary veins of the left atrium, andeven more particularly in the superior pulmonary veins.

[0025] Less-invasive percutaneous catheter ablation techniques have beendisclosed which use end-electrode catheter designs with the intention ofablating and thereby treating focal arrhythmias in the pulmonary veins.These ablation procedures are typically characterized by the incrementalapplication of electrical energy to the tissue to form focal lesionsdesigned to terminate the inappropriate arrhythmogenic conduction.

[0026] One example of a focal ablation method intended to treat focalarrhythmia originating from a pulmonary vein is disclosed byHaissaguerre, et al. in “Right and Left Atrial Radiofrequency CatheterTherapy of Paroxysmal Atrial Fibrillation” in Journal of CardiovascularElectrophysiology 7(12), pp. 1132-1144 (1996). Haissaguerre, et al.discloses radiofrequency catheter ablation of drug-refractory paroxysmalatrial fibrillation using linear atrial lesions complemented by focalablation targeted at arrhythmogenic foci in a screened patientpopulation. The site of the arrhythmogenic foci were generally locatedjust inside the superior pulmonary vein, and the focal ablations weregenerally performed using a standard 4 mm tip single ablation electrode.

[0027] Another focal ablation method of treating atrial arrhythmias isdisclosed in Jais et al., “A focal source of atrial fibrillation treatedby discrete radiofrequency ablation,” Circulation 95:572-576 (1997).Jais et al. discloses treating patients with paroxysmal arrhythmiasoriginating from a focal source by ablating that source. At the site ofarrhythmogenic tissue, in both right and left atria, several pulses of adiscrete source of radiofrequency energy were applied in order toeliminate the fibrillatory process.

[0028] Other assemblies and methods have been disclosed addressing focalsources of arrhythmia in pulmonary veins by ablating circumferentialregions of tissue either along the pulmonary vein, at the ostium of thevein along the atrial wall, or encircling the ostium and along theatrial wall. More detailed examples of device assemblies and methods fortreating focal arrhythmia as just described are disclosed the followingreferences: U.S. Pat. No. 6,117,101 to Diederich et al.; U.S. Pat. No.6,024,740 to Lesh et al.; U.S. Pat. No. 6,012,457 to Lesh; and U.S. Ser.Nos. 09/384,727 and 09/642,251 each entitled “Device and Method forForming a Circumferential Conduction Block in a Pulmonary Vein” toMichael D. Lesh. The disclosures of these references are hereinincorporated in their entirety by reference thereto.

[0029] Another specific device assembly and method which is intended totreat focal atrial fibrillation by ablating a circumferential region oftissue between two seals in order to form a conduction block to isolatean arrhythmogenic focus within a pulmonary vein is disclosed in U.S.Pat. No. 5,938,660 to Swartz et al. and a related Published PCT PatentApplication No. WO 99/00064.

[0030] In particular, certain tissue ablation device assemblies thatincorporate ultrasound energy sources have been observed to be highlyefficient and effective for ablating circumferential regions of tissuewhere pulmonary veins extend from atria. However, the efficiency ofultrasonic output from such a source has been observed to be directlyrelated to the structural coupling of the transducer to the underlyingdelivery member or catheter shaft. The transducer output is dampedwhenever it is in contact with any sort of mounting means between theback or inner side of the transducer and the catheter shaft, evenaccording to known modes using elastomeric mounting structuressandwiched between the transducer and the shaft. Several knownultrasound transducer mounting examples provide support structures thatextend between the transducer and the underlying support member, suchthat for example the transducer rests on the support member which restson the delivery member. Further more detailed examples of suchultrasound transducer support structures are disclosed in the followingreferences: U.S. Pat. No. 5,606,974 to Castellano; and U.S. Pat. No.5,620,479 to Diederich. Further examples of structural support designsfor ultrasound transducers on catheter shafts are disclosed in publishedPCT Patent Application PCT/US98/09554 (WO98/49957) to Diederich et al..

[0031] Further to the previously disclosed ultrasound transducermounting structures and arrangements, it is desirable for the mountingstructure to provide sufficient support and positioning for thetransducer. It is also desirable that such a mounting structure providesfor air backing between the transducer and the underlying delivery shaftin order to isolate ultrasound transmission radially away from thecatheter shaft and toward tissue surrounding the shaft. It has beenobserved that such air backing helps prevent heat build-up in theregion, as the vibrational ultrasound energy has been observed tosuperheat other materials in contact therewith which absorb the energy(airbacking actually reflects the energy radially outwardly as desired).Therefore, such air backing is particularly desirable for highoperational powers associated with therapeutic ultrasound ablationtransmission. It is also desirable that such a mounting structureadequately supports the transducer while minimizing the vibrationaldamping of the transducer during operation. The present inventionaddresses these desires.

SUMMARY OF THE INVENTION

[0032] The present invention provides various improved catheterconstructions and associated methods of manufacture for mounting anultrasound transducer onto a catheter shaft while minimizing the dampingof the transducer associated with the structural coupling. In several ofthe construction variations, the transducer is suspended about an innermember (e.g., the catheter body) absent any support structure betweenthe catheter and the transducer along the length of the transducer. Thatis, transducer mounting is accomplished without the use of internalmounting members and/or elastic member in the space between the innermember and the transducer. Such mounting arrangements support thetransducer and are attached to the inner member (or to an assembly ofmembers) at points proximal and distal of the ultrasound transducer.

[0033] In one mode of the present invention, an ultrasound ablationapparatus is provided with reduced transducer damping. The apparatuscomprises an elongate catheter body having proximal and distal endportions, an outer wall and an outer diameter; a cylindrical ultrasoundtransducer coaxially disposed over the catheter body, the ultrasoundtransducer having proximal and distal end portions, an inner wall and aninner diameter which is greater than the outer diameter of the catheterbody. Consequently, an air gap is provided in a radial separationbetween the inner wall of the ultrasound transducer and the catheterbody. The apparatus also includes a support structure for suspending theultrasound transducer in a substantially fixed coaxial position relativeto the catheter body. The support structure contacts the outer wall ofthe catheter body at locations proximal and distal to the proximal anddistal end portions of the ultrasound transducer, respectively.Accordingly, the support structure holds the ultrasound transducerwithout contacting the inner wall of the ultrasound transducer, therebymaintaining the radial separation while reducing transducer damping.

[0034] In one preferred mode of the ultrasound ablation apparatus, theultrasound transducer is shaped to ablate a circumferential region oftissue. The transducer may include at least one transmissive panel.

[0035] In another aspect of the ultrasound ablation apparatus, at leasta substantial portion of the radial separation is sealed by the supportstructure to prevent external fluids from entering the radialseparation. A gas may be sealed within the radial separation.Alternatively, a liquid maybe sealed within the radial separation.

[0036] The ultrasound ablation apparatus of the present invention mayinclude first and second flanges extending axially from the proximal anddistal end portions of the ultrasound transducer, respectively, thesupport structure being coupled to the first and second flanges. Thesupport structure may comprise first and second elastomeric O-ringsdisposed on the catheter body such that the first and second O-ringsengage the first and second flanges. In a variation of this mode, thesupport structure may comprises first and second sleeves disposed on thecatheter body and fitted over the first and second flanges, to securethe ultrasound transducer relative to the catheter body. In anothervariation, the support structure may comprise first and second splinesdisposed on the catheter body such that the first and second splinesengage the first and second flanges. Alternatively, the supportstructure may comprise first and second annular members disposed alongthe catheter body such that the first and second annular members engagethe first and second flanges.

[0037] In another aspect of the present invention, the support structuremay comprise first and second annular members disposed on the catheterbody, wherein the first and second annular members frictionally engagethe proximal and distal end portions of the ultrasound transducer. Thesupport structure could also comprise a shrink-wrap cover layer disposedaround the ultrasound transducer.

[0038] In one preferred embodiment, the ultrasound ablation apparatus ofthe present invention may include an expandable member adapted to engagea circumferential region of tissue. In this mode, the ultrasoundtransducer is located inside the expandable member and acousticallycoupled to the expandable member. The expandable member may be aninflatable balloon.

[0039] In a variation to the expandable member embodiment, theultrasound ablation apparatus may also have a cooling chamber betweenthe ultrasound transducer and the expandable member. The cooling chamberis adapted to allow a cooling fluid to flow over said ultrasoundtransducer. Further, this mode may include a source of pressurizedcooling fluid and a cooling fluid lumen in the catheter body. The lumenmay have a distal port opening into the cooling chamber. The ultrasoundablation apparatus may also incorporate a thermocouple for monitoringtemperature along at least a portion of the circumferential region oftissue engaged by the expandable member.

[0040] The ultrasound ablation apparatus of the present invention mayalso include at least one electrical lead coupled to the ultrasoundtransducer.

[0041] In a variation of the mounting structure, the apparatus maycomprise fillets located proximal and distal to proximal and distal endportions of the ultrasound transducer for sealing the radial separationfrom entry of external fluids and providing a smooth surface forinsertion of said ultrasound ablation apparatus into a body structure.

[0042] In another variation, the ultrasound ablation apparatus mayinclude a guidewire lumen extending through at least a portion of thecatheter body for slidably engaging a guidewire.

[0043] In another variation to the present invention, the appartus maycomprise an elongate catheter body; and an cylindrical ultrasoundtransducer having first and second ends and inner and outer surfaces.The ultrasound transducer is mounted coaxially on the catheter body suchthat a radial separation is provided between the ultrasound transducerand the catheter body for mechanically isolating the ultrasoundtransducer from the catheter body. In this mode, the support structureis coupled to the ultrasound transducer and the catheter body tomaintain at least a region of the radial separation for reducingacoustic damping caused by the support structure.

[0044] In variations to this mode, annular end members may be providedwith a metallic exterior surface adapted to engage the inner surface ofthe ablation element. This mounting mode may also include an annularintermediate portion, located between the first and second annularmembers and the catheter body.

[0045] In another variation, the support structure may comprise asubstantially tubular member disposed over the catheter body. Thetubular member has proximal and distal end regions and an intermediateregion. The proximal and distal end regions are formed with a largerdiameter than the intermediate region. The ultrasound transducer isdisposed over the intermediate region such that it is axially containedby the proximal and distal end regions.

[0046] In another variation, the support structure may comprise at leastone mandrel extending axially along the catheter body The at least onemandrel engages the catheter body and the inner surface of theultrasound ablation element. The at least one mandrel may be a polyimidetube. More preferably, the at least one mandrel comprises a plurality ofpolyimide tubes positioned substantially uniformly around the catheterbody within the radial separation.

[0047] In another variation, the support structure may comprise abraided metal tubular member disposed around the catheter body such thatthe radial separation is maintained therebetween. The ultrasoundtransducer is mounted coaxially over the braided tubular member.Alternatively, the support structure may include two braided metaltubular members disposed around the catheter body with an axial gaptherebetween. The ultrasound transducer may be mounted to the braidedtubular members thereby bridging the axial gap.

[0048] In another aspect of the invention, the support structure maycomprise two truncated conical members, each having a first end with alarge diameter and a second end with a small diameter. The conicalmembers are disposed over the catheter body such that the first endsface inward and the second ends face outward. The inner surface of theultrasound transducer is engaged by the first ends of the conicalmembers.

[0049] In accordance with another mode of the invention, the supportstructure may comprise an expandable member disposed over the catheterbody and having an outer surface. The inner surface of the ultrasoundtransducer may then be coaxially engaged by the outer surface of theexpandable member.

[0050] The modes of the invention are generally adapted to capture air,or another gas as would be apparent to one of ordinary skill, within themounting structures in order to “air back” the transducer. That is,these modes of suspension maintain an air gap between the transducer andthe catheter shaft in order to maximize radially outward propagation ofthe ultrasound waves, as introduced above. In addition, the air spacedesirably is sealed to prevent fluid infiltration, be it blood oranother fluid.

[0051] According to further beneficial modes, the ultrasound transducerapparatus and method modes just summarized are applied in acircumferential ablation device assembly which is adapted to couple toand ablate a circumferential region of tissue at a location where apulmonary vein extends from an atrium. Moreover, the modes described foruse with a circumferential ultrasound transducer may also be adapted foruse with non-circumferential types of transducers, such as incorporatingpanel transducers that also benefit by being air backed without mountingmembers physically located and extending between such transducers and anunderlying catheter shaft.

[0052] For purposes of summarizing the invention and the advantagesachieved over the prior art, certain objects and advantages of theinvention have been described above and are described below. Of course,it is to be understood that not necessarily all such objects oradvantages may be achieved in accordance with any particular mode of theinvention. Thus, for example, those skilled in the art will recognizethat the invention may be embodied or carried out in a manner thatachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other objects or advantages as maybe taught or suggested herein.

[0053] All of these embodiments are intended to be within the scope ofthe invention herein disclosed. These and other embodiments of thepresent invention will become readily apparent to those skilled in theart from the following detailed description of the preferred embodimentshaving reference to the attached figures, the invention not beinglimited to any particular preferred embodiment(s) disclosed. Inaddition, further aspects, advantages and features of the invention willbecome apparent from the following descriptions of the preferred modesof incorporating an ultrasound transducer onto a delivery element.

BRIEF DESCRIPTION OF THE DRAWINGS

[0054]FIG. 1 diagrammatically shows sequential, general steps fortreating atrial arrhythmia.

[0055] FIGS. 2A-E show schematic, perspective views of variousexemplifying circumferential conduction blocks formed in pulmonary veinwall tissue with a circumferential ablation device assembly.

[0056]FIG. 3 shows a flow diagram of a method for using acircumferential ablation device assembly.

[0057]FIG. 4 shows a perspective view of a circumferential ablationdevice assembly during use in a left atrium subsequent to performingtranseptal access and guidewire positioning steps according to themethod of FIG. 3.

[0058]FIG. 5 shows a similar perspective view of the circumferentialablation device assembly shown in FIG. 4, and further shows acircumferential ablation catheter during use in ablating acircumferential region of tissue along a pulmonary vein wall to form acircumferential conduction block in the pulmonary vein according to themethod of FIG. 3.

[0059]FIG. 6A shows a similar perspective view as shown in FIG. 5,although showing a further circumferential ablation catheter variationwhich is adapted to allow for blood perfusion from the pulmonary veinand into the atrium while performing the circumferential ablation methodshown diagrammatically in FIG. 3.

[0060]FIG. 6B is an enlarged partial view of the circumferentialablation catheter shown in FIG. 6A, with a perfusion lumen shown inphantom.

[0061]FIG. 7 shows a similar perspective view of the left atrium as thatshown in FIGS. 3-5, although showing a cross-sectional view of acircumferential lesion after being formed by circumferential catheterablation according to the method of FIG. 3.

[0062] FIGS. 8A-B show perspective views of another circumferentialablation catheter variation during use in a left atrium according to themethod of FIG. 3, wherein

[0063]FIG. 8A shows a radially compliant expandable member with aworking length adjusted to a radially expanded position while in theleft atrium, and

[0064]FIG. 8B shows the expandable member after advancing it into andengaging a pulmonary vein ostium while in the radially expandedposition.

[0065]FIG. 8C shows the same perspective view of the left atrium shownin FIGS. 8A-B, although shown after forming a circumferential conductionblock according to the circumferential ablation procedure of FIG. 3 andalso after removing the circumferential ablation device assembly fromthe left atrium.

[0066]FIG. 8D shows another circumferential ablation catheter during usein a left atrium, and shows an expandable member in a radially expandedposition which is engaged within a pulmonary vein ostium such that acircumferential band of a circumferential ablation elementcircumscribing the expandable member is also engaged to acircumferential path of tissue along the left posterior atrial wallwhich surrounds the pulmonary vein ostium.

[0067]FIG. 8E shows one particular expandable member and circumferentialablation element which is adapted for use according to the mode of useshown in FIG. 8D.

[0068]FIG. 8F shows a resulting circumferential conduction block orlesion which may be formed with the assemblies shown in FIGS. 8D-E andaccording to the method of use shown in FIG. 8D.

[0069]FIG. 9A diagrammatically shows a method for using acircumferential ablation device assembly to form a circumferentialconduction block in a pulmonary vein in combination with a method forforming long linear lesions between pulmonary vein ostia in aless-invasive “maze”-type procedure.

[0070]FIG. 9B shows a perspective view of a segmented left atrium afterforming several long linear lesions between adjacent pairs of pulmonaryvein ostia according to the method of FIG. 9A.

[0071]FIG. 9C shows a similar perspective view as that shown in FIG. 9B,although showing a circumferential ablation device assembly during usein forming a circumferential lesion in a pulmonary vein which intersectswith two linear lesions that extend into the pulmonary vein, accordingto the method of FIG. 9A.

[0072]FIG. 9D shows a perspective view of another ablation catheterwhich combines a linear ablation member extending between two anchorswith a circumferential ablation member for use in forming acircumferential lesion which intersects with at least one linear lesionaccording to the method of FIG. 9A.

[0073]FIG. 9E shows a perspective view of another circumferentialablation catheter for use in forming a circumferential lesion thatintersects with at least one linear lesion according to the method ofFIG. 9A.

[0074]FIG. 9F shows a perspective view of a segmented left posterioratrial wall with a lesion pattern which results from combining theformation of two linear lesions according to FIG. 9B with the formationof a circumferential conduction block according to the methods anddevices shown in FIGS. 8A-C.

[0075]FIG. 9G shows a perspective view of a segmented left posterioratrial wall with a lesion pattern which results from combining theformation of two linear lesions according to FIG. 9B with the formationof a circumferential conduction block according to the methods anddevices shown in FIGS. 8D-F.

[0076]FIG. 9H shows a schematic perspective view of a left posterioratrial wall with one complete lesion pattern in a variation of aless-invasive “maze”-type procedure wherein circumferential conductionblocks are formed along circumferential paths of tissue along a leftposterior atrial wall such that each circumferential conduction blocksurrounds a pulmonary vein ostium, each pair of vertically adjacentcircumferential conduction blocks intersects, and each pair ofhorizontally adjacent circumferential conduction blocks are connectedwith one of two linear lesions extending between the respective pair ofhorizontally adjacent pulmonary vein ostia.

[0077]FIG. 10 diagrammatically shows a further method for using thecircumferential ablation device assembly of the present invention toform a circumferential conduction block in a pulmonary vein wall,wherein signal monitoring and “post-ablation” test elements are used tolocate an arrhythmogenic origin along the pulmonary vein wall and totest the efficacy of a circumferential conduction block in the wall,respectively.

[0078] FIGS. 11A-B show perspective views of another circumferentialablation member variation for use in a circumferential ablation deviceassembly for pulmonary vein isolation, showing a circumferentialablation electrode circumscribing the working length of an expandablemember with a secondary shape along the longitudinal axis of the workinglength which is a modified step shape, the expandable member being shownin a radially collapsed position and also in a radially expandedposition, respectively.

[0079] FIGS. 11C-D show perspective views of two circumferentialablation electrodes which form equatorial or otherwise circumferentiallyplaced bands that circumscribe the working length of an expandablemember and that have serpentine and sawtooth secondary shapes,respectively, relative to the longitudinal axis of the expandable memberwhen adjusted to a radially expanded position.

[0080] FIGS. 12A-B show perspective views of another circumferentialablation element which includes a plurality of individual ablationelectrodes that are spaced circumferentially to form an equatorial bandwhich circumscribes the working length of an expandable member either inan equatorial location or an otherwise circumferential location that isbounded both proximally and distally by the working length, and whichare adapted to form a continuous circumferential lesion while theworking length is adjusted to a radially expanded position.

[0081]FIG. 13 shows a cross-sectional view of another circumferentialablation member for use in a circumferential ablation device assemblyfor pulmonary vein isolation, wherein the circumferential ablationelement circumscribes an outer surface of an expandable membersubstantially along its working length and is insulated at both theproximal and the distal ends of the working length to thereby form anuninsulated equatorial band in a middle region of the working length orotherwise circumferential region of the working length which is boundedboth proximally and distally by end portions of the working length,which member is adapted to ablate a circumferential path of tissueengaged by the equatorial band.

[0082]FIG. 14 shows a perspective view of another circumferentialablation member which is adapted for use in a circumferential ablationdevice assembly for pulmonary vein isolation, wherein the expandablemember is shown to be a cage of coordinating wires which are adapted tobe adjusted from a radially collapsed position to a radially expandedposition in order to engage electrode elements on the wires about acircumferential pattern of tissue to be ablated.

[0083]FIG. 15 shows a cross-sectional view of another circumferentialablation element which is adapted for use in a circumferential ablationdevice assembly for pulmonary vein isolation. A superelastic, loopedelectrode element is shown at the distal end of a pusher and is adaptedto circumferentially engage pulmonary vein wall tissue to form acircumferential lesion as a conduction block that circumscribes thepulmonary vein lumen.

[0084]FIG. 16A shows a longitudinal cross-sectional view of anothercircumferential ablation catheter, and shows the ablation element toinclude a single cylindrical ultrasound transducer which is positionedalong an inner member within an expandable balloon which is furthershown in a radially expanded condition.

[0085]FIG. 16B shows a transverse cross-sectional view of thecircumferential ablation catheter shown in FIG. 16A taken along line16B-16B shown in FIG. 16A.

[0086]FIG. 16C shows a transverse cross-sectional view of thecircumferential ablation catheter shown in FIG. 16A taken along line16C-16C shown in FIG. 16A.

[0087]FIG. 16D shows a perspective view of the ultrasonic transducer ofFIG. 16A in isolation.

[0088]FIG. 16E shows a modified version of the ultrasonic transducer ofFIG. 16D with individually driven sectors.

[0089]FIG. 17A shows a perspective view of a similar circumferentialablation catheter to the catheter shown in FIG. 16A, and shows thedistal end portion of the circumferential ablation catheter during onemode of use in forming a circumferential conduction block in a pulmonaryvein in the region of its ostium along a left atrial wall (shown incross-section in shadow).

[0090]FIG. 17B shows a similar perspective and cross-section shadow viewof a circumferential ablation catheter and pulmonary vein ostium as thatshown in FIG. 17A, although shows another circumferential ablationcatheter wherein the balloon has a tapered outer diameter.

[0091]FIG. 17C shows a similar view to that shown in FIGS. 17A-B,although showing another circumferential ablation catheter wherein theballoon has a “pear”-shaped outer diameter with a contoured surfacealong a taper which is adapted to seat in the ostium of a pulmonaryvein.

[0092]FIG. 17D shows a cross-sectional view of one circumferentialconduction block which may be formed by use of a circumferentialablation catheter such as that shown in FIG. 17C.

[0093]FIG. 18A shows a cross-sectional view of the distal end portion ofanother circumferential ablation catheter, wherein an outer shield orfilter is provided along the balloon's outer surface in order to form apredetermined shape for the circumferential ablation element created bysonic transmissions from the inner ultrasound transducer.

[0094]FIG. 18B shows a similar view as that shown in FIG. 18A, althoughshowing the distal end portion of another circumferential ablationcatheter which includes a heat sink as an equatorial band within thecircumferential path of energy emission from an inner ultrasoundtransducer.

[0095]FIG. 19A shows a transverse cross-sectional view of an additionalcircumferential ablation catheter for pulmonary vein isolation, andshows the ablation element to include a single transducer sector segmentwhich is positioned along an inner member within an expandable balloonwhich is further shown in a radially expanded condition.

[0096]FIG. 19B shows a transverse cross-sectional view of an additionalcircumferential ablation catheter for pulmonary vein isolation, andshows the ablation element to include a single curvilinear section thatis mounted so as to position its concave surface facing in a radiallyoutward direction.

[0097]FIG. 20A is a perspective view of one embodiment of the suspendedcoaxial transducer.

[0098]FIG. 20B is a cross-sectional view through the transducer (lineB-B).

[0099]FIG. 21A is a perspective view showing another embodiment of thesuspended coaxial transducer having a thin molded shell.

[0100]FIG. 21B shows the transducer in a molded shell in transversesection along plane B-B of FIG. 21A.

[0101]FIG. 22 shows another variation of the mounting design having asupport sleeve and shrink-wrap cover.

[0102]FIG. 23 shows another variation of the design for mounting themolded transducer having an O-ring and shrink-wrap cover.

[0103]FIG. 24 shows another variation of the suspended coaxialtransducer having preformed end mounts.

[0104]FIG. 25A shows a mounting balloon variation of the suspendedcoaxial transducer.

[0105]FIG. 25B is a perspective view of the sequence of making theballoon mounted transducer shown in FIG. 25A.

[0106]FIG. 26 is a partial cross-sectional view of a transducersupported on a support member that is mounted on a tracking member of acatheter assembly.

[0107]FIG. 27 is a perspective view of the support illustrated in FIG.26.

[0108]FIG. 28A is a side view of the support of FIG. 27.

[0109]FIG. 28B is a end view of the support of FIG. 27.

[0110]FIG. 29A shows a perspective view of another transducer mountedonto a tracking member of a catheter assembly according to theinvention.

[0111]FIG. 29B shows a longitudinal cross-sectional view taken alonglines 29B-29B in FIG. 29A.

[0112]FIG. 29C shows a transverse cross-sectional view taken along lines29C-29C in FIG. 29A.

[0113]FIG. 30A is a longitudinal cross-sectional view of a modificationof the support illustrated in FIG. 27.

[0114]FIG. 30B is a longitudinal cross-sectional view of two of thesupport members illustrated in FIG. 30A supporting a transducer on atracking member of a catheter assembly.

[0115]FIG. 31A is a partial longitudinal sectional view of amodification of the transducer and support shown in FIG. 30B.

[0116]FIG. 31B is a longitudinal sectional view of a modification of theembodiment shown in FIG. 31A.

[0117]FIG. 32A is an elevational view of a modification of the ablationcatheter illustrated in FIG. 16, having a splined support (shown inphantom) supporting a transducer relative to an inner member and havingjackets covering the proximal and distal ends of the transducer.

[0118]FIG. 32B is a partial longitudinal sectional view of the cathetershown in FIG. 32A.

[0119]FIG. 33A is a partial longitudinal sectional view of amodification of the catheter shown in FIG. 32A having a splined supportsupporting a transducer relative to an inner member.

[0120]FIG. 33B is a partial longitudinal sectional view of the cathetershown in FIG. 33A illustrating a cooling assembly installed to thecatheter shown in FIG. 33A.

[0121]FIG. 33C is a schematic view of the catheter cooling assemblyillustrated in FIG. 33B disposed within an expandable ablation balloon(shown in phantom).

[0122]FIG. 34A is a modification of the catheter shown in FIG. 32Ahaving a plurality of mandrels arranged between an inner member and atransducer of a catheter so as to maintain a gap between the innersurface of the transducer and an outer surface of the inner member.

[0123]FIG. 34B is a partial longitudinal sectional view of the cathetershown in FIG. 34A with lead wires connected to the electrodes of thetransducer.

[0124]FIG. 35 is a longitudinal sectional view of anothercircumferential ablation catheter, and shows the ablation element toinclude a single cylindrical ultrasound transducer which is positionedalong an inner member and is connected to the inner member via a pair ofend mounts, one end mount being provided at each of the proximal anddistal ends of the transducer.

[0125]FIG. 36 is a longitudinal sectional view of a modification of thecatheter illustrated in FIG. 35 showing the transducer being supportedby a pair of end mounts which are, in turn, supported by a pair ofraised portions of a flexible material bonded to the inner member.

[0126]FIG. 37A is a partial longitudinal sectional view of a furthercircumferential ablation catheter, and shows the ablation element toinclude a single cylindrical ultrasound transducer which is positionedalong an inner member and connected to the inner member via a supportwhich includes metal surface portions in contact with the proximal anddistal ends of the transducer.

[0127]FIG. 37B is a modification of the catheter shown in FIG. 37A, thesupport being formed in two separate pieces.

[0128]FIG. 38 is a longitudinal sectional view of a modification of theablation catheter shown in FIG. 37A.

[0129]FIG. 38B is an enlarged, partial, longitudinal, cross-sectionalview of a modification of the catheter shown in FIG. 38A illustrating analternative structure for connecting the transducer to the metal surfaceportion.

[0130]FIG. 39A is a side elevational view of two metallic bands that maybe used in the catheter illustrated in FIGS. 38A and 38B.

[0131]FIG. 39B is a partial longitudinal sectional view of amodification of the catheter shown in FIG. 37A utilizing the metallicbands illustrated in FIG. 39A.

[0132]FIG. 40 shows a longitudinal sectional view of yet a furthermodification of the catheter shown in FIG. 37A including a singlecylindrical ultrasound transducer positioned along an inner member andbeing supported by a pair of trumpet-shaped metallic bands.

[0133]FIG. 41 shows a longitudinal cross-sectional view of amodification of the catheter illustrated in FIG. 38A having a pair ofmetallic bands bonded to an outer surface of the transducer.

[0134]FIG. 42A is yet another modification of the catheter illustratedin FIG. 38A having a braided metal support being welded to an innersurface of the transducer.

[0135]FIG. 42B is a modification of the catheter shown in FIG. 42Awherein the portion of the braided metal support that extends betweenthe proximal and distal ends of the transducer is removed.

[0136]FIG. 43A shows a longitudinal, cross-sectional view of anothermodification of the catheter shown in FIG. 38A where a mounting assemblyincludes metallic bands sealed to the inner member with a flexiblematerial and shows an expandable balloon which is illustrated in aradially expanded condition.

[0137]FIG. 43B is an enlarged view of a modification of the transducermounting system illustrated in FIG. 43A.

[0138]FIG. 44 is a longitudinal sectional view of a furthercircumferential ablation catheter, and shows the ablation element toinclude a single cylindrical ultrasound transducer which is positionedalong an inner member assembly having raised portions connected to theproximal and distal ends of an ultrasound transducer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0139] As will be described with reference to the detailed embodimentsbelow, the modes for mounting a circumferential ultrasound ablationelement to a catheter shaft according to the present invention arebelieved to be well-suited for use in a circumferential ablation deviceassembly. This device is particularly well-suited for treating patientswith atrial arrhythmia by ablating a circumferential region of tissue ata location where a pulmonary vein extends from an atrium. Specifically,this device can be advantageously used to treat atrial arrhythmia byablating a circumferential region of tissue at a location (a) wherecardiac tissue extends up into the vein, (b) along the vein's ostiumalong the atrial wall, or (c) along the atrial wall and surrounding thevein's ostium. By ablating such a circumferential region of tissue, acircumferential conduction block is formed which either isolates theatrium from an arrhythmogenic focus upstream of the conduction blockrelative to the vein, or ablates the focus.

[0140] This circumferential pulmonary vein ablation aspect of theinvention is therefore also well-suited for use in combination oraggregation with, or where appropriate in substitution for, the variousfeatures and embodiments disclosed in the following references that alsoaddress circumferential ablation at a location where a pulmonary veinextends from an atrium: U.S. Pat. No. 6,024,740 to Lesh et al.; U.S.Pat. No. 6,012,457 to Lesh; U.S. Pat. No. 6,117,101 to Diederich; andU.S. Ser. Nos. 09/384,727 and 09/642,251 each entitled “DEVICE ANDMETHOD FOR FORMING A CIRCUMFERENTIAL CONDUCTION BLOCK IN A PULMONARYVEIN” to Lesh. The disclosures of these references are hereinincorporated in their entirety by reference thereto. For the purpose offurther illustration, particular embodiments for pulmonary veinisolation that are known in the art are shown and described by referenceto FIGS. 1-19B, with the related method of treatment broadly illustratedin diagrammatical form in the flow diagram of FIG. 1.

[0141] The terms “circumference” or “circumferential”, includingderivatives thereof, are herein intended to mean a continuous path orline which forms an outer border or perimeter that surrounds and therebydefines an enclosed region of space. Such a continuous path starts atone location along the outer border or perimeter, and translates alongthe outer border or perimeter until it is completed at the originalstarting location to enclose the defined region of space. The relatedterm “circumscribe,” including derivatives thereof, is herein intendedto mean to enclose, surround, or encompass a defined region of space.Therefore, according to these defined terms, a continuous line which istraced around a region of space and which starts and ends at the samelocation “circumscribes” the region of space and has a “circumference”which is defined by the distance the line travels as it translates alongthe path circumscribing the space.

[0142] Still further, a circumferential path or element may include oneor more of several shapes, and may be, for example, circular, oblong,ovular, elliptical, or otherwise planar enclosures. A circumferentialpath may also be three dimensional, such as, for example, twoopposite-facing semi-circular paths in two different parallel oroff-axis planes which are connected at their ends by line segmentsbridging between the planes.

[0143] For purpose of further illustration, FIGS. 2A-D therefore showvarious circumferential paths A, B, C, and D, respectively, eachtranslating along a portion of a pulmonary vein wall and circumscribinga defined region of space, shown at a, b, c, and d also respectively,each circumscribed region of space being a portion of a pulmonary veinlumen. For still further illustration of the three-dimensionalcircumferential case shown in FIG. 2D, FIG. 2E shows an explodedperspective view of circumferential path D as it circumscribesmultiplanar portions of the pulmonary vein lumen shown at d′, d″, andd′″, which together make up region d as shown in FIG. 2D.

[0144] The term “transect”, including derivatives thereof, is alsoherein intended to mean to divide or separate a region of space intoisolated regions. Thus, each of the regions circumscribed by thecircumferential paths shown in FIGS. 2A-D transects the respectivepulmonary vein, including its lumen and its wall, to the extent that therespective pulmonary vein is divided into a first longitudinal regionlocated on one side of the transecting region, shown, for example, atregion “X” in FIG. 2A, and a second longitudinal region on the otherside of the transecting plane, shown, for example, at region “Y” also inFIG. 2A.

[0145] Therefore, a “circumferential conduction block” according to thepresent invention is formed along a region of tissue which follows acircumferential path along the pulmonary vein wall, circumscribing thepulmonary vein lumen and transecting the pulmonary vein relative toelectrical conduction along its longitudinal axis. The transectingcircumferential conduction block therefore isolates electricalconduction between opposite longitudinal portions of the pulmonary wallrelative to the conduction block and along the longitudinal axis.

[0146] The terms “ablate” or “ablation,” including derivatives thereof,are hereafter intended to mean the substantial altering of themechanical, electrical, chemical, or other structural nature of tissue.In the context of intracardiac ablation applications shown and describedwith reference to the variations of the illustrative embodiment below,“ablation” is intended to mean sufficient altering of tissue propertiesto substantially block conduction of electrical signals from or throughthe ablated cardiac tissue.

[0147] The term “element” within the context of “ablation element” isherein intended to mean a discrete element, such as an electrode, or aplurality of discrete elements, such as a plurality of spacedelectrodes, which are positioned so as to collectively ablate a regionof tissue.

[0148] Therefore, an “ablation element” according to the defined termsmay include a variety of specific structures adapted to ablate a definedregion of tissue. For example, one suitable ablation element for use inthe present invention may be formed, according to the teachings of theembodiments below, from an “energy emitting” type which is adapted toemit energy sufficient to ablate tissue when coupled to and energized byan energy source. Suitable “energy emitting” ablation elements for usein the present invention may therefore include, for example: anelectrode element adapted to couple to a direct current (“DC”) oralternating current (“AC”) current source, such as a radiofrequency(“RF”) current source; an antenna element which is energized by amicrowave energy source; a heating element, such as a metallic elementor other thermal conductor which is energized to emit heat such as byconvective or conductive heat transfer, by resistive heating due tocurrent flow, or by optical heating with light; a light emittingelement, such as a fiber optic element which transmits light sufficientto ablate tissue when coupled to a light source; or an ultrasonicelement such as an ultrasound crystal element which is adapted to emitultrasonic sound waves sufficient to ablate tissue when coupled to asuitable excitation source.

[0149] In addition, other elements for altering the nature of tissue maybe suitable as “ablation elements” under the present invention whenadapted according to the detailed description of the invention below.For example, a cryoablation element adapted to sufficiently cool tissueto substantially alter the structure thereof may be suitable if adaptedaccording to the teachings of the current invention. Furthermore, afluid delivery element, such as a discrete port or a plurality of portswhich are fluidly coupled to a fluid delivery source, may be adapted toinfuse an ablating fluid, such as a fluid containing alcohol, into thetissue adjacent to the port or ports to substantially alter the natureof that tissue.

[0150] The term “diagnose”, including derivatives thereof, is intendedto include patients suspected or predicted to have atrial arrhythmia, inaddition to those having specific symptoms or mapped electricalconduction indicative of atrial arrhythmia.

[0151] Returning to the inventive method as shown in FIG. 1, a patientdiagnosed with atrial arrhythmia according to diagnosing step (1) istreated with a circumferential conduction block according to treatmentstep (2). In one aspect, a patient diagnosed according to diagnosis step(1) with multiple wavelet arrhythmia originating from multiple regionsalong the atrial wall may also be treated in part by forming thecircumferential conduction block according to treatment step (2),although as an adjunct to forming long linear regions of conductionblock between adjacent pulmonary vein ostia in a less-invasive“maze”-type catheter ablation procedure. More detail regarding thisparticular aspect of the inventive method is provided below withreference to a combination circumferential-long linear lesion ablationdevice which is described below with reference to FIGS. 9A-F.

[0152] In another aspect of the method of FIG. 1, a patient diagnosedwith focal arrhythmia originating from an arrhythmogenic origin or focusin a pulmonary vein is treated according to this method when thecircumferential conduction block is formed along a circumferential pathof wall tissue that either includes the arrhythmogenic origin or isbetween the origin and the left atrium. In the former case, thearrhythmogenic tissue at the origin is destroyed by the conduction blockas it is formed through that focus. In the latter case, thearrhythmogenic focus may still conduct abnormally, although suchaberrant conduction is prevented from entering and affecting the atrialwall tissue due to the intervening circumferential conduction block.

[0153] In still a further aspect of the method shown in FIG. 1, thecircumferential conduction block may be formed in one of several waysaccording to treatment step (2). In 30 one example not shown, thecircumferential conduction block may be formed by a surgical incision orother method to mechanically transect the pulmonary vein, followed bysuturing the transected vein back together. As the circumferentialinjury is naturally repaired, such as through a physiologic scarringresponse common to the “maze” procedure, electrical conduction willgenerally not be restored across the injury site. In another example notshown, a circumferential conduction block of one or more pulmonary veinsmay be performed in an epicardial ablation procedure, wherein anablation element is either placed around the target pulmonary vein or istranslated circumferentially around it while being energized to ablatethe adjacent tissue in an “outside-in” approach. This alternative methodmay be performed during an open chest-type procedure, or may be doneusing other known epicardial access techniques.

[0154]FIG. 3 diagrammatically shows the sequential steps of a method forusing a circumferential ablation device assembly to form acircumferential conduction block in a pulmonary vein. Thecircumferential ablation method according to FIG. 3 includes:positioning a circumferential ablation element at an ablation regionalong the pulmonary vein according to a series of detailed steps showncollectively in FIG. 3 as positioning step (3); and thereafter ablatinga continuous circumferential region of tissue in the PV wall at theablation region according to ablation step (4).

[0155] Further to positioning step (3) according to the method of FIG.3, a distal tip of a guiding catheter is first positioned within theleft atrium according to a transeptal access method, which is furtherdescribed in more detail as follows. The right venous system is firstaccessed using the “Seldinger” technique, wherein a peripheral vein(such as a femoral vein) is punctured with a needle, the puncture woundis dilated with a dilator to a size sufficient to accommodate anintroducer sheath, and an introducer sheath with at least one hemostaticvalve is seated within the dilated puncture wound while maintainingrelative hemostasis. With the introducer sheath in place, the guidingcatheter or sheath is introduced through the hemostatic valve of theintroducer sheath and is advanced along the peripheral vein, into theregion of the vena cavae, and into the right atrium.

[0156] Once in the right atrium, the distal tip of the guiding catheteris positioned against the fossa ovalis in the intraatrial septal wall. A“Brockenbrough” needle or trocar is then advanced distally through theguide catheter until it punctures the fossa ovalis. A separate dilatormay also be advanced with the needle through the fossa ovalis to preparean access port through the septum for seating the guiding catheter. Theguiding catheter thereafter replaces the needle across the septum and isseated in the left atrium through the fossa ovalis, thereby providingaccess for object devices through its own inner lumen and into the leftatrium.

[0157] It is however further contemplated that other left atrial accessmethods may be suitable substitutes for using a circumferential ablationdevice assembly for pulmonary vein isolation. In one alternativevariation not shown, a “retrograde” approach may be used, wherein theguiding catheter is advanced into the left atrium from the arterialsystem. In this variation, the Seldinger technique is employed to gainvascular access into the arterial system, rather than the venous, forexample, at a femoral artery. The guiding catheter is advancedretrogradedly through the aorta, around the aortic arch, into theventricle, and then into the left atrium through the mitral valve.

[0158] Subsequent to gaining transeptal access to the left atrium asjust described, positioning step (3) according to FIG. 3 next includesadvancing a guidewire into a pulmonary vein, which is done generallythrough the guiding catheter seated in the fossa ovalis. In addition tothe left atrial access guiding catheter, the guidewire according to thisvariation may also be advanced into the pulmonary vein by directing itinto the vein with a second sub-selective delivery catheter (not shown)which is coaxial within the guiding catheter, such as, for example, byusing one of the directional catheters disclosed in U.S. Pat. No.5,575,766 to Swartz. Or, the guidewire may have sufficient stiffness andmaneuverability in the left atrial cavity to unitarily subselect thedesired pulmonary vein distally of the guiding catheter seated at thefossa ovalis.

[0159] Suitable guidewire designs for use in the overall circumferentialablation device assembly described may be selected from previously knowndesigns, while generally any suitable choice should include a shaped,radiopaque distal end portion with a relatively stiff, torquableproximal portion adapted to steer the shaped tip under X-rayvisualization. Guidewires having an outer diameter ranging from 0.010″to 0.035″ may be suitable. In cases where the guidewire is used tobridge the atrium from the guiding catheter at the fossa ovalis, andwhere no other sub-selective guiding catheters are used, guidewireshaving an outer diameter ranging from 0.018″ to 0.035″ may be required.It is believed that guidewires within this size range may be required toprovide sufficient stiffness and maneuverability in order to allow forguidewire control and to prevent undesirable guidewire prolapsing withinthe relatively open atrial cavity.

[0160] Subsequent to gaining pulmonary vein access, positioning step (3)of FIG. 3 next includes tracking the distal end portion of acircumferential ablation device assembly over the guidewire and into thepulmonary vein, followed by positioning a circumferential ablationelement at an ablation region of the pulmonary vein where thecircumferential conduction block is to be desirably formed.

[0161] FIGS. 4-5 further show a circumferential ablation device assembly(100) during use in performing positioning step (3) and ablation step(4) just described with reference to FIG. 3. Included in thecircumferential ablation device assembly (100) are guiding catheter(101), guidewire (102), and circumferential ablation catheter (103).

[0162] More specifically, FIG. 4 shows guiding catheter (101) subsequentto performing a transeptal access method according to FIG. 3, and alsoshows guidewire (102) subsequent to advancement and positioning within apulmonary vein, also according to step (3) of FIG. 3. FIG. 4 showscircumferential ablation catheter (103) as it tracks coaxially overguidewire (102) with a distal guidewire tracking member, which isspecifically shown only in part at first and second distal guidewireports (142,144) located on the distal end portion (132) of an elongatecatheter body (130). A guidewire lumen (not shown) extends between thefirst and second distal guidewire ports (142,144) and is adapted toslidably receive and track over the guidewire. In the particularvariation of FIG. 4, the second distal guidewire port (142) is locatedon a distal end portion (132) of the elongate catheter body (130),although proximally of first distal guidewire port (142).

[0163] As would be apparent to one of ordinary skill, the distalguidewire tracking member shown in FIG. 4 and just described may beslidably coupled to the guidewire externally of the body in a“backloading” technique after the guidewire is first positioned in thepulmonary vein. Furthermore, there is no need in this guidewire trackingvariation for a guidewire lumen in the proximal portions of the elongatecatheter body (130), which allows for a reduction in the outer diameterof the catheter shaft in that region. Nevertheless, it is furthercontemplated that a design which places the second distal guidewire porton the proximal end portion of the elongate catheter body would also beacceptable, as is described below, for example, with reference to theperfusion embodiment of FIGS. 6A-B.

[0164] In addition, the inclusion of a guidewire lumen extending withinthe elongate body between first and second ports, as provided in FIG. 4,should not limit the scope of acceptable guidewire tracking members.Other guidewire tracking members which form a bore adapted to slidablyreceive and track over a guidewire are also considered acceptable, suchas, for example, the structure adapted to engage a guidewire asdescribed in U.S. Pat. No. 5,505,702 to Arney.

[0165] While the assemblies and methods shown variously throughout theFigures include a guidewire coupled to a guidewire tracking member onthe circumferential ablation catheter, other detailed variations mayalso be suitable for positioning the circumferential ablation element atthe ablation region in order to form a circumferential conduction blockthere. For example, an alternative circumferential ablation catheter notshown may include a “fixedwire”-type of design wherein a guidewire isintegrated into the ablation catheter as one unit. In anotheralternative assembly, the same type of sub-selective sheaths describedabove with reference to U.S. Pat. No. 5,575,766 to Swartz for advancinga guidewire into a pulmonary vein may also be used for advancing acircumferential ablation catheter device across the atrium and into apulmonary vein.

[0166]FIG. 4 also shows circumferential ablation catheter (103) with acircumferential ablation element (160) formed on an expandable member(170). The expandable member (170) is shown in FIG. 4 in a radiallycollapsed position adapted for percutaneous translumenal delivery intothe pulmonary vein according to positioning step (3) of FIG. 3. However,expandable member (170) is also adjustable to a radially expandedposition when actuated by an expansion actuator (175), as shown in FIG.5. Expansion actuator (175) may include, but is not limited to, apressurizeable fluid source. According to the expanded state shown inFIG. 5, expandable member (170) includes a working length L relative tothe longitudinal axis of the elongate catheter body which has a largerexpanded outer diameter OD than when in the radially collapsed position.Furthermore, the expanded outer diameter OD is sufficient tocircumferentially engage the ablation region of the pulmonary vein.Therefore, the terms “working length” are herein intended to mean thelength of an expandable member which, when in a radially expandedposition, has an expanded outer diameter that is: (a) greater than theouter diameter of the expandable member when in a radially collapsedposition; and (b) sufficient to engage a body space wall or adjacentablation region surrounding the expandable member, at least on twoopposing internal sides of the body space wall or adjacent ablationregion, with sufficient surface area to anchor the expandable member.

[0167] Circumferential ablation element (160) also includes acircumferential band (152) on the outer surface of working length Lwhich is coupled to an ablation actuator (190) at a proximal end portionof the elongate catheter body (shown schematically). After expandablemember (170) is adjusted to the radially expanded position and at leasta portion of working length L circumferentially engages the pulmonaryvein wall in the ablation region, the circumferential band (152) of thecircumferential ablation element (160) is actuated by ablation actuator(190) to ablate the surrounding circumferential path of tissue in thepulmonary vein wall, thereby forming a circumferential lesion thatcircumscribes the pulmonary vein lumen and transects the electricalconductivity of the pulmonary vein to block conduction in a directionalong its longitudinal axis.

[0168]FIG. 6A shows another circumferential ablation catheter (203)during use also according to the method of FIG. 3, wherein a perfusionlumen (260) (shown in phantom in FIG. 6B) is formed within the distalend portion (232) of elongate catheter body (230). The perfusion lumen(260) in this example is formed between a distal perfusion port, whichin this example is the first distal guidewire port (242), and proximalperfusion port (244). Proximal perfusion port (244) is formed throughthe wall of the elongate catheter body (230) and communicates with theguidewire lumen (not shown) which also forms the perfusion lumen betweenthe distal and proximal perfusion ports. In the particular design shown,after the guidewire has provided for the placement of the ablationelement into the pulmonary vein, the guidewire is withdrawn proximallyof the proximal perfusion port (244) (shown schematically in shadow) sothat the lumen between the ports is clear for antegrade blood flow intothe distal perfusion port (242), proximally along the perfusion lumen,out the proximal perfusion port (244) and into the atrium (perfusionflow shown schematically with arrows).

[0169] Further to the perfusion design shown in FIGS. 6A-B, guidewire(102) is positioned in a guidewire lumen which extends the entire lengthof the elongate catheter body (230) in an “over-the-wire”-type ofdesign, which facilitates the proximal withdrawal of the guidewire toallow for perfusion while maintaining the ability to subsequentlyre-advance the guidewire distally through the first distal guidewireport (242) for catheter repositioning. In one alternative variation notshown, the guidewire is simply withdrawn and disengaged from the seconddistal guidewire port (244), in which case the circumferential ablationcatheter must generally be withdrawn from the body in order to re-couplethe distal guidewire tracking member with the guidewire.

[0170] In another alternative perfusion variation not shown which is amodification of the embodiment of FIG. 6A, a proximal perfusion port isprovided as a separate and distinct port positioned between the seconddistal guidewire port (244) and the expandable member (270), whichallows for proximal withdrawal of the guidewire to clear the guidewirelumen and thereby form a perfusion lumen between the first distalguidewire port and the proximal perfusion port. The guidewire of thisalternative variation, however, remains engaged within the guidewirelumen between the second distal guidewire port and the proximalperfusion port.

[0171] Passive perfusion during expansion of the expandable member isbelieved to minimize stasis and allow the target pulmonary vein tocontinue in its atrial filling function during the atrial arrhythmiatreatment procedure. Without this perfusion feature, the expandablemember when in the radially expanded position during ablation blocks theflow from the vein into the atrium, which flow stasis may result inundesirable thrombogenesis in the pulmonary vein distally to theexpandable member. In addition, in cases where the ablation element isadapted to ablate tissue with heat conduction at the ablation region, asdescribed by reference to more detailed embodiments below, the perfusionfeature according to the variation of FIGS. 6A-B may also provide acooling function in the surrounding region, including in the bloodadjacent to the expandable member.

[0172] Moreover, in addition to the specific perfusion structure shownand described by reference to FIGS. 6A-B, it is to be further understoodthat other structural variants which allow for perfusion flow duringexpansion of the expandable element may provide suitable substitutesaccording to one of ordinary skill.

[0173]FIG. 7 shows pulmonary vein (52) after removing thecircumferential ablation device assembly subsequent to forming acircumferential lesion (70) around the ablation region of the pulmonaryvein wall (53) according to the use of the circumferential ablationdevice assembly shown in stepwise fashion in FIGS. 3-6. Circumferentiallesion (70) is shown located along the pulmonary vein adjacent to thepulmonary vein ostium (54), and is shown to also be “transmural,” whichis herein intended to mean extending completely through the wall, fromone side to the other. Also, the circumferential lesion (70) is shown inFIG. 7 to form a “continuous” circumferential band, which is hereinintended to mean without gaps around the pulmonary vein wallcircumference, thereby circumscribing the pulmonary vein lumen.

[0174] It is believed, however, that circumferential catheter ablationwith a circumferential ablation element according to various uses of theultrasound ablation element structures of the present invention mayleave some tissue, either transmurally or along the circumference of thelesion, which is not actually ablated, but which is not substantialenough to allow for the passage of conductive signals. Therefore, theterms “transmural” and “continuous” as just defined are intended to havefunctional limitations, wherein some tissue in the ablation region maybe unabated but there are no functional gaps which allow forsymptomatically arrhythmogenic signals to conduct through the conductionblock and into the atrium from the pulmonary vein.

[0175] Moreover, it is believed that the functionally transmural andcontinuous lesion qualities just described are characteristic of acompleted circumferential conduction block in the pulmonary vein. Such acircumferential conduction block thereby transects the vein, isolatingconduction between the portion of the vein on one longitudinal side ofthe lesion and the portion on the other side. Therefore, any foci oforiginating arrhythmogenic conduction which is opposite the conductionblock from the atrium is prevented by the conduction block fromconducting down into the atrium and atrial arrhythmic affects aretherefore nullified.

[0176] FIGS. 8A-B show a further circumferential ablation member (350)that includes a radially compliant expandable member (370) which isadapted to conform to a pulmonary vein ostium (54) at least in part byadjusting it to a radially expanded position while in the left atriumand then advancing it into the ostium. FIG. 8A shows expandable member(370) after being adjusted to a radially expanded position while locatedin the left atrium (50). FIG. 8B further shows expandable member (370)after being advanced into the pulmonary vein (52) until at least aportion of the expanded working length L of circumferential ablationmember (350), which includes a circumferential band (352), engages thepulmonary vein ostium (54). FIG. 8C shows a portion of a circumferentiallesion (72) which forms a circumferential conduction block in the regionof the pulmonary vein ostium (54) subsequent to actuating thecircumferential ablation element to form the circumferential lesion.

[0177] In addition to conforming to the pulmonary vein ostium,expandable member (370) is also shown in FIG. 8B to engage acircumferential path of tissue along the left posterior atrial wallwhich surrounds ostium (54). Moreover, circumferential bank (352) of thecircumferential ablation member is also thereby adapted to engage thatatrial wall tissue. Therefore, the circumferential conduction blockformed according to the method shown and just described in sequentialsteps by reference to FIGS. 8A-B, as shown in-part in FIG. 8C, includesablating the circumferential path of atrial wall tissue which surroundsostium (54). Accordingly, the entire pulmonary vein, including theostium, is thereby electrically isolated from at least a substantialportion of the left atrial wall which includes the other of thepulmonary vein ostia, as would be apparent to one of ordinary skillaccording to the sequential method steps shown in FIGS. 8A-B and byfurther reference to the resulting circumferential lesion (72) shown inFIG. 8C.

[0178] FIGS. 8D-E show another highly beneficial circumferentialablation device embodiment and use thereof for electrically isolatingpulmonary vein and ostium from a substantial portion of the leftposterior atrial wall. However, unlike the embodiment previously shownand described by reference to FIGS. 8A-C, the FIGS. 8D-E embodimentisolates the pulmonary vein without also ablating tissue along the lumenor lining of the pulmonary vein or ostium, as is apparent by referenceto the resulting circumferential conduction block shown in FIG. 8F.

[0179] In more detail, FIG. 8D shows a similar device assembly as thatshown in FIGS. 8A-B, except that circumferential band (352′) has ageometry (primarily width) and position along expandable member (370′)such that it is adapted to engage only a circumferential path of tissuealong the left posterior atrial wall which surrounds the pulmonary veinostium. In one aspect of this embodiment, the compliant nature of theexpandable member may be self-conforming to the region of the ostiumsuch that the circumferential band is placed against this atrial walltissue merely by way of conformability.

[0180] In another variation, a “pear”-shaped expandable member orballoon that includes a contoured taper may be suitable for useaccording to the FIG. 8D embodiment, as is shown by way of example inFIG. 8E. Such a pear shape may be preformed into the expandable memberor balloon, or the member may be adapted to form this shape by way ofcontrolled compliance as it expands, such as for example by the use ofcomposite structures within the balloon construction. In any case,according to the “pear”-shaped variation, the circumferential band(352′) of the ablation member is preferably placed along the surface ofthe contoured taper which is adapted to face the left posterior atrialwall during use according to the method illustrated by FIG. 8D. It isfurther contemplated that the ablation element may be further extendedor alternatively positioned along other portions of the taper, such asis shown by example in shadow at extended band (352″) in FIG. 8E.Accordingly, the variation shown in FIG. 8E to include extended band(352″) may also adapt this particular device embodiment for use informing circumferential conduction blocks also along tissue within thepulmonary vein and ostium, such as according to the previously describedmethod shown in FIGS. 8A-C.

[0181] The method of forming a circumferential conduction block along acircumferential path of tissue along a left posterior atrial wall andwhich surrounds a pulmonary vein ostium without ablating the tissue ofthe vein or ostium should not be limited to the particular deviceembodiments just illustrated by reference to FIGS. 8D-F. Other devicevariations may be acceptable substitute for use according to thismethod. In one particular example which is believed to be suitable, a“looped” ablation member such as the embodiment illustrated below byreference to FIG. 15 may be adapted to form a “looped” ablation elementwithin the left atrium and then be advanced against the left posterioratrial wall such that the loop engages the circumferential path oftissue along the atrial wall and which surrounds a vein ostium.Thereafter, the looped ablation element may be actuated to ablate theengaged tissue, such as for further illustration like a branding ironforming the predetermined pattern around the pulmonary vein os. Inaddition, other device or method variations may also be suitablesubstitutes according to one of ordinary skill.

[0182] FIGS. 9A-D collectively show a circumferential ablation deviceassembly as it is used to form a circumferential conduction blockadjunctively to the formation of long linear lesions in a less-invasive“maze”-type procedure, as introduced above for the treatment ofmultiwavelet reentrant type fibrillation along the left atrial wall.

[0183] More specifically, FIG. 9A diagrammatically shows a summary ofsteps for performing a “maze”-type procedure by forming circumferentialconduction blocks that intersect with long linear conduction blocksformed between the pulmonary veins. As disclosed in copending patentapplication (Application Number not yet assigned) entitled “TissueAblation Device and Method of Use” filed by Michael Lesh, M.D. on May 9,1997, which is herein incorporated in its entirety by reference thereto,a box-like conduction block surrounding an arrhythmogenic atrial wallregion bounded by the pulmonary veins may be created by forming longlinear lesions between anchors in all pairs of adjacent pulmonary veinostia, such as is shown in part in steps (5) and (6) of FIG. 9A.However, it is further believed that, in some particular applications,such linear lesions may be made sufficiently narrow with respect to thesurface area of the pulmonary vein ostia that they may not intersect,thereby leaving gaps between them which may present proarrhythmicpathways for abnormal conduction into and from the box, such as is shownbetween linear lesions (57,58) in FIG. 9B. Therefore, by forming thecircumferential conduction block according to step (7) of FIG. 9A, andas shown by use of circumferential ablation member (450) in FIG. 9C, thelinear lesions are thereby bridged and the gaps are closed.

[0184] In a further variation to the specific embodiments shown in FIGS.9B-C, FIG. 9D shows another circumferential ablation device assemblywhich includes both circumferential and linear ablation elements(452,461), respectively. Circumferential ablation member (450) is shownto include an expandable member (470) which is adjusted to a radiallyexpanded position that is asymmetric to the underlying catheter shaft.Linear ablation member (460) extends along the elongate body proximallyfrom the circumferential ablation member (450). When expandedsufficiently to engage the pulmonary vein wall, expandable member (470)provides at least a portion of an anchor for a first end (462) of linearablation member (460).

[0185] A shaped stylet (466) is shown in shadow in FIG. 9D within theelongate catheter body in the region of the second end (464) of thelinear ablation member (460). Shaped stylet (466) is adapted to push thesecond end (464) into an adjacent pulmonary vein ostium such that thelinear ablation member (460) is adapted to substantially contact theleft atrial wall between the adjacent vein ostia to form the linearablation according to the method of FIG. 9A. In addition to the use ofshaped stylet (466), it is further contemplated that a second anchor maybe used adjacent to second end (464), such as for example anintermediate guidewire tracking member adapted to track over a guidewireengaged to the pulmonary vein, as shown in FIG. 9E at intermediateguidewire tracking member (466′) which is engaged over guidewire (469).

[0186] Moreover, the method shown schematically in FIG. 9A and also invarious detail by reference to FIGS. 9B-C provides a specific sequenceof steps for the purpose of illustration. According to this illustrativesequence, the linear lesions are formed first and then are connectedthereafter with the circumferential conduction block. However, acircumferential conduction block may be formed prior to the formation ofthe linear lesions or conduction blocks, or in any other combination orsub-combination of sequential steps, so long as the resultingcombination of lesions allows for the circumferential block to intersectwith and connect with the linear lesions. In addition, thecircumferential conduction block which connects the linear lesions mayalso include a circumferential path of tissue which surrounds andelectrically isolates the pulmonary vein ostium from the rest of theleft posterior atrial wall, such as for example by considering theembodiments just shown and described by reference to FIGS. 9A-E in viewof the embodiment previously shown and described in relation to FIG. 8Cabove.

[0187] In addition to the particular embodiments just shown anddescribed by reference to FIGS. 9A-E, other methods are alsocontemplated for combining circumferential and linear conduction blocksdevice assemblies and uses in order to perform a less-invasive“maze”-type procedure. For example, FIG. 9F shows one particular lesionpattern which results by combining a circumferential conduction block,formed according to the previous embodiments of FIGS. 8A-C, with a pairof linear lesions which are formed according to the method illustratedby FIG. 9B. In a further example shown in FIG. 9G, another lesionpattern is formed by combining the pair of linear lesions of FIG. 9Bwith a circumferential conduction block formed according to theembodiments which are previously illustrated above by reference to FIGS.9D-F. While the resulting lesion patterns of FIGS. 9F and 9G differslightly as regards the particular geometry and position of thecircumferential conduction block formed, the two variations are alsosimilar in that the circumferential conduction block includes acircumferential path of atrial wall tissue. When such circumferentialconduction blocks are formed between adjacent pulmonary vein ostia,shorter linear lesions are therefore sufficient to bridge thecircumferential lesions during the overall “maze”-type procedure.

[0188] To this end, according to one contemplated less-invasive“maze”-type procedure (not shown) wherein multiple circumferentialconduction blocks are formed in atrial wall tissue such that eachpulmonary vein ostium is surrounded by and is electrically isolated withone circumferential conduction block. A series of four linear lesionsmay be formed between the various pairs of adjacent ostia and with justsufficient length to intersect with and bridge the correspondingadjacent circumferential blocks. A box-like conduction block is therebyformed by the four circumferential conduction blocks and the fourbridging linear lesions. A fifth linear lesion may be also formedbetween at least a portion of the box-like conduction block and anotherpredetermined location, such as for example the mitral value annulus.

[0189]FIG. 9H shows yet a further variation for forming circumferentialconduction blocks along atrial wall tissue around the pulmonary veinostia during a less invasive “maze”-type procedure. According to thisfurther variation, the circumferential conduction block patterns formedaround each of two adjacent superior and inferior pulmonary vein ostiaare shown in FIG. 9H to intersect, thereby alleviating the need for alinear lesion in order to form a conduction block between the ostia.Furthermore, the distances between the inferior and superior ostia, bothon the right and left side of the posterior atrial wall, are believed tobe significantly shorter than the distances between the two adjacentsuperior or inferior ostia. Therefore, FIG. 9H only shows theoverlapping circumferential conduction blocks as just described to bepositioned vertically between the inferior-superior pairs of adjacentostia, and further shows linear lesions which are used to connect theright and left sided ostia of the superior and inferior pairs. In someinstances these linear lesions will not be required to cure, treat orprevent a particular atrial arrhythmia condition. However, othercombinations of these patterns are further contemplated, such as forexample using only overlapping circumferential conduction blocks betweenall adjacent pairs of ostia in order to form the entire “maze”-type leftatrial pattern.

[0190]FIG. 10 diagrammatically shows a further method for using acircumferential ablation device assembly wherein electrical signalsalong the pulmonary vein are monitored with a sensing element before andafter ablation according to steps (8) and (9), respectively. Signalswithin the pulmonary vein are monitored prior to forming a conductionblock, as indicated in step (8) in FIG. 10, in order to confirm that thepulmonary vein chosen contains an arrhythmogenic origin for atrialarrhythmia. Failure to confirm an arrhythmogenic origin in the pulmonaryvein, particularly in the case of a patient diagnosed with focalarrhythmia, may dictate the need to monitor signals in another pulmonaryvein in order to direct treatment to the proper location in the heart.In addition, monitoring the pre-ablation signals may be used to indicatethe location of the arrhythmogenic origin of the atrial arrhythmia,which information helps determine the best location to form theconduction block. As such, the conduction block may be positioned toinclude and therefore ablate the actual focal origin of the arrhythmia,or may be positioned between the focus and the atrium in order to blockaberrant conduction from the focal origin and into the atrial wall.

[0191] In addition or in the alternative to monitoring electricalconduction signals in the pulmonary vein prior to ablation, electricalsignals along the pulmonary vein wall may also be monitored by thesensing element subsequent to circumferential ablation, according tostep (9) of the method of FIG. 10. This monitoring method aids intesting the efficacy of the ablation in forming a complete conductionblock against arrhythmogenic conduction. Arrhythmogenic firing from theidentified focus will not be observed during signal monitoring along thepulmonary vein wall when taken below a continuous circumferential andtransmural lesion formation, and thus would characterize a successfulcircumferential conduction block. In contrast, observation of sucharrhythmogenic signals between the lesion and the atrial wallcharacterizes a functionally incomplete or discontinuous circumference(gaps) or depth (transmurality) which would potentially identify theneed for a subsequent follow-up procedure, such as a secondcircumferential lesioning procedure in the ablation region.

[0192] A test electrode may also be used in a “post ablation” signalmonitoring method according to step (10) of FIG. 10. In one particularembodiment not shown, the test electrode is positioned on the distal endportion of an elongate catheter body and is electrically coupled to acurrent source for firing a test signal into the tissue surrounding thetest electrode when it is placed distally or “upstream” of thecircumferential lesion in an attempt to simulate a focal arrhythmia.This test signal generally challenges the robustness of thecircumferential lesion in preventing atrial arrhythmia from any suchfuture physiologically generated aberrant activity along the suspectvein.

[0193] Further to the signal monitoring and test stimulus methods justdescribed, such methods may be performed with a separate electrode orelectrode pair located on the catheter distal end portion adjacent tothe region of the circumferential ablation element, or may be performedusing one or more electrodes which form the circumferential ablationelement itself, as will be further developed below.

[0194] Circumferential Ablation Members

[0195] The designs for an expandable member and circumferential ablationelement for use in a circumferential ablation device assembly have beendescribed generically with reference to the embodiments shown in theprevious Figures. Examples of more specific expandable member andablation element embodiments which are adapted for use in such ablationdevice assemblies are further provided as follows.

[0196] Notwithstanding their somewhat schematic detail, thecircumferential ablation members shown in the previous figures doillustrate one particular embodiment wherein a circumferential electrodeelement circumscribes an outer surface of an expandable member. Theexpandable member of the embodiments shown may take one of severaldifferent forms, although the expandable member is generally hereinshown as an inflatable balloon that is coupled to an expansion actuator(175) which is a pressurizeable fluid source. The balloon is preferablymade of a polymeric material and forms a fluid chamber whichcommunicates with a fluid passageway (not shown in the figures) thatextends proximally along the elongate catheter body and terminatesproximally in a proximal fluid port that is adapted to couple to thepressurizeable fluid source.

[0197] In one expandable balloon variation, the balloon is constructedof a relatively inelastic plastics (e.g., polymers or monomers) such asa polyethylene (“PE”; preferably linear low density or high density orblends thereof), polyolefin copolymer (“POC”), polyethylene terepthalate(“PET”), polyimide, or a nylon material. In this construction, theballoon has a low radial yield or compliance over a working range ofpressures and may be folded into a predetermined configuration whendeflated in order to facilitate introduction of the balloon into thedesired ablation location via known percutaneous catheterizationtechniques. In this variation, one balloon size may not suitably engageall pulmonary vein walls for performing the circumferential ablationmethods herein described on all needy patients. Therefore, it is furthercontemplated that a kit of multiple ablation catheters, with eachballoon working length having a unique predetermined expanded diameter,may be provided from which a treating physician may choose a particulardevice to meet a particular patient's pulmonary vein anatomy.

[0198] In an alternative expandable balloon variation, the balloon isconstructed of a relatively compliant, elastomeric material, such as,for example (but not limited to), a silicone, latex, polyurethane, ormylar elastomer. In this construction, the balloon takes the form of atubular member in the deflated, non-expanded state. When the elastictubular balloon is pressurized with fluid such as in the previous,relatively non-compliant example, the material forming the wall of thetubular member elastically deforms and stretches radially to apredetermined diameter for a given inflation pressure. It is furthercontemplated that the compliant balloon may be constructed as acomposite, such as, for example, a latex or silicone balloon skin whichincludes fibers, such as metal, Kevlar, or nylon fibers, which areembedded into the skin. Such fibers, when provided in a predeterminedpattern such as a mesh or braid, may provide a controlled compliancealong a preferred axis, preferably limiting longitudinal compliance ofthe expandable member while allowing for radial compliance.

[0199] It is believed that, among other features, the relativelycompliant variation may provide a wide range of working diameters, whichmay allow for a wide variety of patients, or of vessels within a singlepatient, to be treated with just one or a few devices. Furthermore, thisrange of diameters is achievable over a relatively low range ofpressures, which is believed to diminish a potentially traumatic vesselresponse that may otherwise be presented concomitant with higherpressure inflations, particularly when the inflated balloon is oversizedto the vessel. In addition, the low-pressure inflation feature of thisvariation is suitable because the functional requirement of theexpandable balloon is merely to engage the ablation element against acircumferential path along the inner lining of the pulmonary vein wall.

[0200] Moreover, a circumferential ablation member is adapted to conformto the geometry of the pulmonary vein ostium, at least in part byproviding substantial compliance to the expandable member, as was shownand described previously by reference to FIGS. 8A-B. Further to thisconformability to pulmonary vein ostium as provided in the specificdesign of FIGS. 8A-B, the working length L of expandable member (370) isalso shown to include a taper which has a distally reducing outerdiameter from a proximal end (372) to a distal end (374). In either acompliant or the non-compliant balloon, such a distally reducing taperedgeometry adapts the circumferential ablation element to conform to thefunneling geometry of the pulmonary veins in the region of their ostiain order to facilitate the formation of a circumferential conductionblock there.

[0201] Further to the circumferential electrode element embodiment asshown variously throughout the previous illustrative Figures, thecircumferential electrode element is coupled to an ablation actuator(190). Ablation actuator (190) generally includes a radio-frequency(“RF”) current source (not shown) that is coupled to both the RFelectrode element and also a ground patch (195) which is in skin contactwith the patient to complete an RF circuit. In addition, ablationactuator (190) preferably includes a monitoring circuit (not shown) anda control circuit (not shown) which together use either the electricalparameters of the RF circuit or tissue parameters such as temperature ina feedback control loop to drive current through the electrode elementduring ablation. Also, where a plurality of ablation elements orelectrodes in one ablation element are used, a switching means may beused to multiplex the RF current source between the various elements orelectrodes.

[0202] FIGS. 11A-D show various patterns of electrically conductive,circumferential electrode bands as electrode ablation elements, eachcircumscribing an outer surface of the working length of an expandablemember. FIGS. 11A-B show circumferential ablation member (550) toinclude a continuous circumferential electrode band (552) thatcircumscribes an outer surface of an expandable member (570). FIG. 11Bmore specifically shows expandable member (570) as a balloon which isfluidly coupled to a pressurizeable fluid source (175), and furthershows electrode band (circumferential ablation element) (552)electrically coupled via electrically conductive lead (554) to ablationactuator (190). In addition, a plurality of apertures (572) are shown inthe balloon skin wall of expandable member (570) adjacent to electrodeband (552). The purpose of these apertures (572) is to provide apositive flow of fluid such as saline or ringers lactate fluid into thetissue surrounding the electrode band (552). Such fluid flow is believedto reduce the temperature rise in the tissue surrounding the electrodeelement during RF ablation.

[0203] The shapes shown collectively in FIGS. 11A-D allow for acontinuous electrode band to circumscribe an expandable member's workinglength over a range of expanded diameters, a feature which is believedto be particularly useful with a relatively compliant balloon as theexpandable member. In the particular embodiments of FIGS. 11A-D, thisfeature is provided primarily by a secondary shape given to theelectrode band relative to the longitudinal axis of the working lengthof the expandable member. Electrode band (552) is thus shown in FIGS.11A-B to take the specific secondary shape of a modified step curve.Other shapes than a modified step curve are also suitable, such as theserpentine or sawtooth secondary shapes shown respectively in FIGS.11C-D. Other shapes in addition to those shown in FIGS. 11A-D and whichmeet the defined functional requirements are further contemplated.

[0204] In addition, the electrode band provided by the circumferentialablation elements shown in FIGS. 11C-D and also shown schematically inFIGS. 3-6B has a functional band width w relative to the longitudinalaxis of the working length which is only required to be sufficientlywide to form a complete conduction block against conduction along thewalls of the pulmonary vein in directions parallel to the longitudinalaxis. In contrast, the working length L of the respective expandableelement is adapted to securely anchor the distal end portion in placesuch that the ablation element is firmly positioned at a selected regionof the pulmonary vein for ablation. Accordingly, the band width w isrelatively narrow compared to the working length L of the expandableelement, and the electrode band may thus form a relatively narrowequatorial band which has a band width that is less than two-thirds oreven one-half of the working length of the expandable element.Additionally, it is to be noted here and elsewhere throughout thespecification, that a narrow band may be placed at locations other thanthe equator of the expandable element, preferably as long as the band isbordered on both sides by a portion of the working length L.

[0205] In another aspect of the narrow equatorial band variation for thecircumferential ablation element, the circumferential lesion formed mayalso be relatively narrow when compared to its own circumference, andmay be less than two-thirds or even one-half its own circumference onthe expandable element when expanded. In one arrangement which isbelieved to be suitable for ablating circumferential lesions in thepulmonary veins as conduction blocks, the band width w is less than 1 cmwith a circumference on the working length when expanded that is greaterthan 1.5 cm.

[0206] FIGS. 12A-B show a further variation of a circumferentialablation element which is adapted to maintain a continuouscircumferential lesion pattern over a range of expanded diameters andwhich includes electrode elements that form a relatively narrowequatorial band around the working length of an expandable balloonmember. In this variation, a plurality of individual electrode/ablationelements (562) are included in the circumferential ablation element andare positioned in spaced arrangement along an equatorial band whichcircumscribes an outer surface of the expandable member's working lengthL.

[0207] The size and spacing between these individual electrode elements(562), when the balloon is expanded, is adapted to form a substantiallycontinuous circumferential lesion in pulmonary vein wall tissue when inintimal contact adjacent thereto, and is further adapted to form such alesion over a range of band diameters as the working length is adjustedbetween a variety of radially expanded positions. Each individualelectrode element (562) has two opposite ends (563,564), respectively,along a long axis LA and also has a short axis SA, and is positionedsuch that the long axis LA is at an acute angle relative to thelongitudinal axis LA of the elongate catheter body and expandable member(560). At least one of the ends (563,564) along the long axis LAoverlaps with an end of another adjacent individual electrode element,such that there is a region of overlap along their circumferentialaspect, i.e., there is a region of overlap along the circumferentialcoordinates. The terms “region of overlap along their circumferentialcoordinate” are herein intended to mean that the two adjacent ends eachare positioned along the working length with a circumferential and alsoa longitudinal coordinate, wherein they share a common circumferentialcoordinate. In this arrangement, the circumferential compliance alongthe working length which accompanies radial expansion of the expandablemember also moves the individual electrode elements apart along thecircumferential axis. However, the spaced, overlapping arrangementdescribed allows the individual ablation elements to maintain a certaindegree of their circumferential overlap, or at least remain close enoughtogether, such that a continuous lesion may be formed without gapsbetween the elements.

[0208] The construction for suitable circumferential electrode elementsin the RF variations herein described, such as the various electrodeembodiments described with reference to FIGS. 11A-12B, may comprise ametallic material deposited on the outer surface of the working lengthusing conventional techniques, such as by plasma depositing, sputtercoating, chemical vapor deposition, other known techniques which areequivalent for this purpose, or otherwise affixing a metallic shapedmember onto the outer surface of the expandable member such as throughknown adhesive bonding techniques. Other RF electrode arrangements arealso considered, so long as they form a circumferential conduction blockas previously described. For example, a balloon skin may itself bemetallized, such as by mixing conductive metal, including but notlimited to gold, platinum, or silver, with a plastic (e.g., polymer) toform a compounded, conductive matrix as the balloon skin.

[0209] Still further to the RF electrode embodiments, anothercircumferential ablation member variation (not shown) may also includean expandable member, such as an inflatable balloon, that includes aporous skin that is adapted to allow fluid, such as hypertonic salinesolution, to pass from an internal chamber defined by the skin andoutwardly into surrounding tissues. Such a porous skin may beconstructed according to several different methods, such as by formingholes in an otherwise contiguous plastic (e.g., polymeric) material,including mechanically drilling or using laser energy, or the porousskin may simply be an inherently porous membrane. In any case, byelectrically coupling the fluid within the porous balloon skin to an RFcurrent source (preferably monopolar), the porous region of theexpandable member serves as an RF electrode wherein RF current flowsoutwardly through the pores via the conductive fluid. In addition, it isfurther contemplated that a porous outer skin may be provided externallyof another, separate expandable member, such as a separate expandableballoon, wherein the conductive fluid is contained in a region betweenthe porous outer skin and the expandable member contained therein.Various other “fluid electrode” designs than those specifically hereindescribed may also be suitable according to one of ordinary skill uponreview of this disclosure.

[0210] In the alternative, or in addition to the RF electrode variationsjust described, the circumferential ablation element may also includeother ablative energy sources or sinks, and particularly may include athermal conductor that circumscribes the outer circumference of theworking length of an expandable member. Examples of suitable thermalconductor arrangements include a metallic element which may, forexample, be constructed as previously described for the more detailed RFembodiments above. However, in the thermal conductor embodiment such ametallic element would be generally either resistively heated in aclosed loop circuit internal to the catheter, or conductively heated bya heat source coupled to the thermal conductor. In the latter case ofconductive heating of the thermal conductor with a heat source, theexpandable member may be, for example, a plastic (e.g., polymeric)balloon skin which is inflated with a fluid that is heated either by aresistive coil or by bipolar RF current. In any case, it is believedthat a thermal conductor on the outer surface of the expandable memberis suitable when it is adapted to heat tissue adjacent thereto to atemperature between 40° and 80° Celsius.

[0211] Further to the thermal conduction variation for thecircumferential ablation element, the perfusion balloon embodiment asshown in FIGS. 6A-B may be particularly useful in such a design. It isbelieved that ablation through increased temperatures, as provided byexample above may also enhance coagulation of blood in the pulmonaryvein adjacent to the expandable member, which blood would otherwiseremain stagnant without such a perfusion feature.

[0212] One further circumferential ablation element design which isbelieved to be highly useful in performing the ablation methods hereindescribed is shown in FIG. 13 to include a circumferential ablationmember (600) with two insulators (602,604) that encapsulate the proximaland distal ends, respectively, of the working length L of an expandablemember (610). In the particular embodiment shown, the insulators(602,604) are thermal insulators, such as a thermal insulator comprisinga Teflon material. Expandable member (610) is an inflatable balloonwhich has a balloon skin (612) that is thermally conductive tosurrounding tissue when inflated with a heated fluid which may contain aradiopaque agent, saline fluid, ringers lactate, combinations thereof,other known biocompatible fluids having acceptable heat transferproperties for these purposes, further to the thermal conductorembodiments previously described. By providing these spaced insulators,a circumferential ablation element is formed as an equatorial band (603)of uninsulated balloon skin is located between the opposite insulators.In this configuration, the circumferential ablation element is able toconduct heat externally of the balloon skin much more efficiently at theuninsulated equatorial band (603) than at the insulated portions, andthereby is adapted to ablate only a circumferential region of tissue ina pulmonary vein wall which is adjacent to the equatorial band. It isfurther noted that this embodiment is not limited to an “equatorial”placement of the ablation element. Rather, a circumferential band may beformed anywhere along the working length of the expandable member andcircumscribing the longitudinal axis of the expandable member aspreviously described.

[0213]FIG. 13 further shows use of a radiopaque marker (620) to identifythe location of the equatorial band (603) in order to facilitateplacement of that band at a selected ablation region of a pulmonary veinvia X-ray visualization. Radiopaque marker (620) is opaque under X-ray,and may be constructed, for example, of a radiopaque metal such as gold,platinum, or tungsten, or may comprise a radiopaque plastic (e.g.,polymer) such as a metal loaded polymer. FIG. 13 shows radiopaque marker(620) positioned coaxially over an inner tubular member (621) which isincluded in a coaxial catheter design as would be apparent to one ofordinary skill. Such a radiopaque marker may also be combined with theother embodiments herein shown and described. To note, when thecircumferential ablation member which forms an equatorial band includesa metallic electrode element, such electrode may itself be radiopaqueand may not require use of a separate marker as just described.

[0214] The thermal insulator embodiment just described by reference toFIG. 13 is illustrative of a broader embodiment, wherein acircumferential ablation member has an ablating surface along the entireworking length of an expandable member, but is shielded from releasingablative energy into surrounding tissues except for along an unshieldedor uninsulated equatorial band. As such, the insulator embodimentcontemplates other ablation elements, such as the RF embodimentspreviously described above, which are provided along the entire workinglength of an expandable member and which are insulated at their ends toselectively ablate tissue only about an uninsulated equatorial band.

[0215] In a further example using the insulator embodiment incombination with a circumferential RF electrode embodiment, a metallizedballoon which includes a conductive balloon skin may have an electricalinsulator, such as a plastic (e.g., polymeric) coating, at each end ofthe working length and thereby selectively ablate tissue withelectricity flowing through the uninsulated equatorial band. In this andother insulator embodiments, it is further contemplated that theinsulators described may be only partial and still provide theequatorial band result. For instance, in the conductive RF electrodeballoon case, a partial electrical insulator will allow a substantialcomponent of current to flow through the uninsulated portion due to a“shorting” response to the lower resistance in that region.

[0216] In still a further example of an insulator combined with an RFablation electrode, a porous membrane comprises the entire balloon skinof an expandable member. By insulating the proximal and distal endportions of the working length of the expandable member, only the poresin the unexposed equatorial band region are allowed to effuse theelectrolyte which carries an ablative RF current.

[0217] Further to the expandable member design for use in acircumferential ablation member as herein described, other expandablemembers than a balloon are also considered suitable. For example, in oneexpandable cage embodiment shown in FIG. 14, cage (650) comprisescoordinating wires (651) and is expandable to engage a desired ablationregion in a pulmonary vein.

[0218] The radial expansion of cage (650) is accomplished as follows.Sheath (652) is secured around the wires proximally of cage (650).However, core (653), which may be a metallic mandrel such as stainlesssteel, extends through sheath (652) and distally within cage (650)wherein it terminates in a distal tip (656). Wires (651) are secured todistal tip (656), for example, by soldering, welding, adhesive bonding,heat shrinking a plastic (e.g., polymeric) member over the wires, or anycombination of these methods. Core (653) is slidable within sheath(652), and may, for example, be housed within a tubular lumen (notshown) within sheath (652), the wires being housed between a coaxialspace between the tubular lumen and sheath (652). By moving the sheath(652) relative to core (653) and distal tip (656) (shown by arrows inFIG. 14), the cage (650) is collapsible along its longitudinal axis inorder to force an outward radial bias (also shown with arrows in FIG.14) to wires (651) in an organized fashion to formed a working length ofcage (650) which is expanded (not shown).

[0219] Further to the particular expandable cage embodiment shown inFIG. 14, a plurality of ablation electrodes (655) is shown, each beingpositioned on one of wires (651) and being similarly located along thelongitudinal axis of the cage (650). The radial bias given to wires(651) during expansion, together with the location of the ablationelectrodes (655), serves to position the plurality of ablationelectrodes/elements (655) along a circumferential, equatorial band alongthe expanded working length of cage (650). The wires forming a cageaccording to this embodiment may also have another predetermined shapewhen in the radially expanded position. For example, a taper similar tothat shown for expandable member (370) in FIGS. 8A-B may be formed byexpanding cage (650), wherein the ablation element formed by ablationelectrodes (655) may be positioned between the proximal end and thedistal end of the taper.

[0220] Further to the construction of the embodiment shown in FIG. 14,wires (651) are preferably metal, and may comprise stainless steel or asuperelastic metal alloy, such as an alloy of nickel and titanium, or acombination of both. Regarding the case of nickel and titaniumconstruction for wires (655), a separate electrical conductor may berequired in order to actuate ablation electrodes (655) to efficientlyemit ablative current into surrounding tissues. In the case where wires(651) are constructed of stainless steel, they may also serve aselectrical conductors for ablation electrodes (655). Further to thestainless steel design, the wires (651) may be coated with an electricalinsulator to isolate the electrical flow into surrounding tissues at thesite of the ablation electrodes (655). Moreover, the ablation electrodes(655) in the stainless steel wire variation may be formed simply byremoving electrical insulation in an isolated region to allow forcurrent to flow into tissue only from that exposed region.

[0221] In a further cage embodiment (not shown) to that shown in FIG.14, a circumferential strip of electrodes may also be secured to thecage (650) such that the strip circumscribes the cage at a predeterminedlocation along the cage's longitudinal axis. By expanding cage (650) aspreviously described, the strip of electrodes are adapted to take acircumferential shape according to the shape of the expanded cage (650).Such an electrode strip is preferably flexible, such that it may beeasily reconfigured when the cage is adjusted between the radiallycollapsed and expanded positions and such that the strip may be easilyadvanced and withdrawn with the cage within the delivery sheath.Furthermore, the electrode strip may be a continuous circumferentialelectrode such as a conductive spring coil, or may be a flexible stripwhich includes several separate electrodes along its circumferentiallength. In the latter case, the flexible strip may electrically coupleall of the electrodes to a conductive lead that interfaces with a drivecircuit, or each electrode may be separately coupled to one or more suchconductive leads.

[0222] Another circumferential ablation element adapted for use in acircumferential conduction block assembly of the type herein describedis shown in FIG. 15, wherein circumferential ablation member (700)includes a looped member (710) attached, preferably by heat shrinking,to a distal end of a pusher (730). Looped member (710) and pusher (730)are slidably engaged within delivery sheath (750) such that loopedmember (710) is in a first collapsed position when positioned andradially confined within delivery sheath (750), and expands to a secondexpanded position when advanced distally from delivery sheath (750).

[0223] Looped member (710) is shown in more detail in FIG. 15 to includea core (712) which is constructed of a superelastic metal alloy such asa nickel-titanium alloy and which has a looped portion with shape memoryin the looped configuration. This looped configuration is shown in FIG.15 to be in a plane which is off-axis, preferably perpendicular, to thelongitudinal axis of the pusher (730). This off-axis orientation of theloop is adapted to engage a circumferential path of tissue along apulmonary vein wall which circumscribes the pulmonary vein lumen whenthe looped member (710) is delivered from the delivery sheath (750) whenthe delivery sheath is positioned within the vein lumen parallel to itslongitudinal axis. An ablation electrode (714) is also shown in FIG. 15as a metallic coil which is wrapped around core (712) in its loopedportion.

[0224] Pusher (730) is further shown in FIG. 15 to include a tubularpusher member (732) which is heat shrunk over two ends (712′) of core(712) which extend proximally of looped member (710) through pusher(730) in the particular variation shown. While in this embodiment core(712) extends through the pusher in order to provide stiffness to thecomposite design for the pusher, it is further contemplated that thesuperelastic metal of the core may be replaced or augmented in thepusher region with another different mandrel or pusher core (not shown),such as a stiffer stainless steel mandrel. Also shown within pusher(730) is an electrically conductive lead (735) which is coupled to theablation electrode (714) and which is also adapted in a proximal regionof the pusher (not shown) to couple to an ablation actuator (190) suchas an RF current source (shown schematically).

[0225] Ultrasonic Energy Source

[0226] FIGS. 16A-19B show various specific embodiments of a broadercircumferential ablation device assembly that utilizes an ultrasonicenergy source to ablate tissue. The present circumferential ablationdevice has particular utility in connection with forming acircumferential lesion within or about a pulmonary vein ostium or withinthe vein itself in order to form a circumferential conductive block.This application of the present ablation device, however, is merelyexemplifying of one preferred mode of use, and it is understood thatthose skilled in the art can readily adapt the present ablation devicefor applications in other body spaces.

[0227] As common to each of the following embodiments, a source ofacoustic energy is provided for a delivery device that also includes ananchoring mechanism. In one mode, the anchoring mechanism comprises anexpandable member that also positions the acoustic energy source withinthe body; however, other anchoring and positioning devices may also beused, such as, for example, a basket mechanism. In a more specific form,the acoustic energy source is located within the expandable member andthe expandable member is adapted to engage a circumferential path oftissue either about or along a pulmonary vein in the region of itsostium along a left atrial wall. The acoustic energy source in turn isacoustically coupled to the wall of the expandable member and thus tothe circumferential region of tissue engaged by the expandable memberwall by emitting a circumferential and longitudinally collimatedultrasound signal when actuated by an acoustic energy driver. The use ofacoustic energy, and particularly ultrasonic energy, offers theadvantage of simultaneously applying a dose of energy sufficient toablate a relatively large surface area within or near the heart to adesired heating depth without exposing the heart to a large amount ofcurrent. For example, a collimated ultrasonic transducer can form alesion, which has about a 1.5 mm width, about a 2.5 mm diameter lumen,such as a pulmonary vein and of a sufficient depth to form an effectiveconductive block. It is believed that an effective conductive block canbe formed by producing a lesion within the tissue that is transmural orsubstantially transmural. Depending upon the patient as well as thelocation within the pulmonary vein ostium, the lesion may have a depthof 1 millimeter to 10 millimeters. It has been observed that thecollimated ultrasonic transducer can be powered to provide a lesionhaving these parameters so as to form an effective conductive blockbetween the pulmonary vein and the posterior wall of the left atrium.

[0228] With specific reference now to the embodiment illustrated inFIGS. 16A through 16D, a circumferential ablation device assembly (800)includes an elongate body (802) with proximal and distal end portions(810,812), an expandable balloon (820) located along the distal endportion (812) of elongate body (802), and a circumferential ultrasoundtransducer (830) which forms a circumferential ablation member which isacoustically coupled to the expandable balloon (820). In more detail,FIGS. 16A-C variously show elongate body (802) to include guidewirelumen (804), inflation lumen (806), and electrical lead lumen (808). Theablation device, however, can be of a self steering type rather than anover-the-wire type device.

[0229] Each lumen extends between a proximal port (not shown) and arespective distal port, which distal ports are shown as distal guidewireport (805) for guidewire lumen (804), distal inflation port (807) forinflation lumen (806), and distal lead port (809) for electrical leadlumen (808). Although the guidewire, inflation and electrical leadlumens are generally arranged in a side-by-side relationship, theelongate body (802) can be constructed with one or more of these lumensarranged in a coaxial relationship, or in any of a wide variety ofconfigurations that will be readily apparent to one of ordinary skill inthe art.

[0230] In addition, the elongate body (802) is also shown in FIGS. 16Aand 16C to include an inner member (803) which extends distally beyonddistal inflation and lead ports (807,809), through an interior chamberformed by the expandable balloon (820), and distally beyond expandableballoon (820) where the elongate body terminates in a distal tip. Theinner member (803) forms the distal region for the guidewire lumen (804)beyond the inflation and lead ports, and also provides a support memberfor the cylindrical ultrasound transducer (830) and for the distal neckof the expansion balloon, as described in more detail below.

[0231] One more detailed construction for the components of the elongatebody (802) which is believed to be suitable for use in transeptal leftatrial ablation procedures is as follows. The elongate body (802) itselfmay have an outer diameter provided within the range of from about 5French to about 10 French, and more preferable from about 7 French toabout 9 French. The guidewire lumen preferably is adapted to slidablyreceive guidewires ranging from about 0.010 inch to about 0.038 inch indiameter, and preferably is adapted for use with guidewires ranging fromabout 0.018 inch to about 0.035 inch in diameter. Where a 0.035 inchguidewire is to be used, the guidewire lumen preferably has an innerdiameter of 0.040 inch to about 0.042 inch. In addition, the inflationlumen preferably has an inner diameter of about 0.020 inch in order toallow for rapid deflation times, although may vary based upon theviscosity of inflation medium used, length of the lumen, and otherdynamic factors relating to fluid flow and pressure.

[0232] In addition to providing the requisite lumens and support membersfor the ultrasound transducer assembly, the elongate body (802) of thepresent embodiment must also be adapted to be introduced into the leftatrium such that the distal end portion with balloon and transducer maybe placed within the pulmonary vein ostium in a percutaneoustranslumenal procedure, and even more preferably in a transeptalprocedure as otherwise herein provided. Therefore, the distal endportion (812) is preferably flexible and adapted to track over and alonga guidewire seated within the targeted pulmonary vein. In one furthermore detailed construction which is believed to be suitable, theproximal end portion is adapted to be at least 30% more stiff than thedistal end portion. According to this relationship, the proximal endportion may be suitably adapted to provide push transmission to thedistal end portion while the distal end portion is suitably adapted totrack through bending anatomy during in vivo delivery of the distal endportion of the device into the desired ablation region.

[0233] Notwithstanding the specific device constructions just described,other delivery mechanisms for delivering the ultrasound ablation memberto the desired ablation region are also contemplated. For example, whilethe FIG. 16A variation is shown as an “over-the-wire” catheterconstruction, other guidewire tracking designs may be suitablesubstitutes, such as, for example, catheter devices which are known as“rapid exchange” or “monorail” variations wherein the guidewire is onlyhoused coaxially within a lumen of the catheter in the distal regions ofthe catheter. In another example, a deflectable tip design may also be asuitable substitute and which is adapted to independently select adesired pulmonary vein and direct the transducer assembly into thedesired location for ablation. Further to this latter variation, theguidewire lumen and guidewire of the FIG. 16A variation may be replacedwith a “pullwire” lumen and associated fixed pullwire which is adaptedto deflect the catheter tip by applying tension along varied stiffnesstransitions along the catheter's length. Still further to this pullwirevariation, acceptable pullwires may have a diameter within the rangefrom about 0.008 inch to about 0.020 inch, and may further include ataper, such as, for example, a tapered outer diameter from about 0.020inch to about 0.008 inch.

[0234] More specifically regarding expandable balloon (820) as shown invaried detail between FIGS. 16A and 16C, a central region (822) isgenerally coaxially disposed over the inner member (803) and is borderedat its end neck regions by proximal and distal adaptions (824,826). Theproximal adaption (824) is sealed over elongate body (802) proximally ofthe distal inflation and the electrical lead ports (807,809), and thedistal adaption (826) is sealed over inner member (803). According tothis arrangement, a fluid tight interior chamber is formed withinexpandable balloon (820). This interior chamber is fluidly coupled to apressurizeable fluid source (not shown) via inflation lumen (806). Inaddition to the inflation lumen (806), electrical lead lumen (808) alsocommunicates with the interior chamber of expandable balloon (820) sothat the ultrasound transducer (830), which is positioned within thatchamber and over the inner member (803), may be electrically coupled toan ultrasound drive source or actuator, as will be provided in moredetail below.

[0235] The expandable balloon (820) may be constructed from a variety ofknown materials, although the balloon (820) preferably is adapted toconform to the contour of a pulmonary vein ostium. For this purpose, theballoon material can be of the highly compliant variety, such that thematerial elongates upon application of pressure and takes on the shapeof the body lumen or space when fully inflated. Suitable balloonmaterials include elastomers, such as, for example, but withoutlimitation, Silicone, latex, or low durometer polyurethane (for example,a durometer of about 80 A).

[0236] In addition or in the alternative to constructing the balloon ofhighly compliant material, the balloon (820) can be formed to have apredefined fully inflated shape (i.e., be preshaped) to generally matchthe anatomic shape of the body lumen in which the balloon is inflated.For instance, as described below in greater detail, the balloon can havea distally tapering shape to generally match the shape of a pulmonaryvein ostium, and/or can include a bulbous proximal end to generallymatch a transition region of the atrium posterior wall adjacent to thepulmonary vein ostium. In this manner, the desired seating within theirregular geometry of a pulmonary vein or vein ostium can be achievedwith both compliant and non-compliant balloon variations.

[0237] Notwithstanding the alternatives which may be acceptable as justdescribed, the balloon (820) is preferably constructed to exhibit atleast 300% expansion at 3 atmospheres of pressure, and more preferablyto exhibit at least 400% expansion at that pressure. The term“expansion” is herein intended to mean the balloon outer diameter afterpressurization divided by the balloon inner diameter beforepressurization, wherein the balloon inner diameter before pressurizationis taken after the balloon is substantially filled with fluid in ataught configuration. In other words, “expansion” is herein intended torelate to change in diameter that is attributable to the materialcompliance in a stress strain relationship. In one more detailedconstruction which is believed to be suitable for use in most conductionblock procedures in the region of the pulmonary veins, the balloon isadapted to expand under a normal range of pressure such that its outerdiameter may be adjusted from a radially collapsed position of about 5millimeters to a radially expanded position of about 2.5 centimeters (orapproximately 500% expansion ratio).

[0238] The ablation member, which is illustrated in FIGS. 16A-D, takesthe form of annular ultrasonic transducer (830). In the illustratedembodiment, the annular ultrasonic transducer (830) has a unitarycylindrical shape with a hollow interior (i.e., is tubular shaped);however, the transducer applicator (830) can have a generally annularshape and be formed of a plurality of segments. For instance, thetransducer applicator (830) can be formed by a plurality of tube sectorsthat together form an annular shape. The tube sectors can also be ofsufficient arc lengths so as when joined together, the sectors assemblyforms a “clover-leaf” shape. This shape is believed to provide overlapin heated regions between adjacent elements. The generally annular shapecan also be formed by a plurality of planar transducer segments whichare arranged in a polygon shape (e.g., hexagon). In addition, althoughin the illustrated embodiment the ultrasonic transducer comprises asingle transducer element, the transducer applicator can be formed of amulti-element array, as described in greater detail below.

[0239] As is shown in detail in FIG. 16D, cylindrical ultrasoundtransducer (830) includes a tubular wall (831) which includes threeconcentric tubular layers. The central layer (832) is a tubular shapedmember of a piezoceramic or piezoelectric crystalline material. Thetransducer preferably is made of type PZT-4, PZT-5 or PZT-8, quartz orLithium-Niobate type piezoceramic material to ensure high power outputcapabilities. These types of transducer materials are commerciallyavailable from Stavely Sensors, Inc. of East Hartford, Conn., or fromValpey-Fischer Corp. of Hopkinton, Mass.

[0240] The outer and inner tubular members (833,834) enclose centrallayer (832) within their coaxial space and are constructed of anelectrically conductive material. In the illustrated embodiment, thesetransducer electrodes (833, 834) comprise a metallic coating, and morepreferably a coating of nickel, copper, silver, gold, platinum, oralloys of these metals.

[0241] One more detailed construction for a cylindrical ultrasoundtransducer for use in the present application is as follows. The lengthof the transducer (830) or transducer assembly (e.g., multi-elementarray of transducer elements) desirably is selected for a given clinicalapplication. In connection with forming circumferential condition blocksin cardiac or pulmonary vein wall tissue, the transducer length can fallwithin the range of approximately 2 mm up to greater than 10 mm, andpreferably equals about 5 mm to 10 mm. A transducer accordingly sized isbelieved to form a lesion of a width sufficient to ensure the integrityof the formed conductive block without undue tissue ablation. For otherapplications, however, the length can be significantly longer.

[0242] Likewise, the transducer outer diameter desirably is selected toaccount for delivery through a particular access path (e.g.,percutaneously and transeptally), for proper placement and locationwithin a particular body space, and for achieving a desired ablationeffect. In the given application within or proximate of the pulmonaryvein ostium, the transducer (830) preferably has an outer diameterwithin the range of about 1.8 mm to greater than 2.5 mm. It has beenobserved that a transducer with an outer diameter of about 2 mmgenerates acoustic power levels approaching 20 Watts per centimeterradiator or greater within myocardial or vascular tissue, which isbelieved to be sufficient for ablation of tissue engaged by the outerballoon for up to about 2 cm outer diameter of the balloon. Forapplications in other body spaces, the transducer applicator (830) mayhave an outer diameter within the range of about 1 mm to greater than3-4 mm (e.g., as large as 1 to 2 cm for applications in some bodyspaces).

[0243] The central layer (832) of the transducer (830) has a thicknessselected to produce a desired operating frequency. The operatingfrequency will vary of course depending upon clinical needs, such as thetolerable outer diameter of the ablation and the depth of heating, aswell as upon the size of the transducer as limited by the delivery pathand the size of the target site. As described in greater detail below,the transducer (830) in the illustrated application preferably operateswithin the range of about 5 MHz to about 20 MHz, and more preferablywithin the range of about 7 MHz to about 10 MHz. Thus, for example, thetransducer can have a thickness of approximately 0.3 mm for an operatingfrequency of about 7 MHz (i.e., a thickness generally equal to ½ thewavelength associated with the desired operating frequency).

[0244] The transducer (830) is vibrated across the wall thickness and toradiate collimated acoustic energy in the radial direction. For thispurpose, as best seen in FIGS. 16A and 16D, the distal ends ofelectrical leads (836,837) are electrically coupled to outer and innertubular members or electrodes (833,834), respectively, of the transducer(830), such as, for example, by soldering the leads to the metalliccoatings or by resistance welding. In the illustrated embodiment, theelectrical leads are 4-8 mil (0.004 to 0.008 inch diameter) silver wireor the like.

[0245] The proximal ends of these leads are adapted to couple to anultrasonic driver or actuator (840), which is schematically illustratedin FIG. 16D. FIGS. 16A-D further show leads (836,837) as separate wireswithin electrical lead lumen (808), in which configuration the leadsmust be well insulated when in close contact. Other configurations forleads (836,837) are therefore contemplated. For example, a coaxial cablemay provide one cable for both leads which is well insulated as toinductance interference. Or, the leads may be communicated toward thedistal end portion (812) of the elongate body through different lumenswhich are separated by the catheter body.

[0246] The transducer also can be sectored by scoring or notching theouter transducer electrode (833) and part of the central layer (832)along lines parallel to the longitudinal axis L of the transducer (830),as illustrated in FIG. 16E. A separate electrical lead connects to eachsector in order to couple the sector to a dedicated power control thatindividually excites the corresponding transducer sector. By controllingthe driving power and operating frequency to each individual sector, theultrasonic driver (840) can enhance the uniformity of the ultrasonicbeam around the transducer (830), as well as can vary the degree ofheating (i.e., lesion control) in the angular dimension.

[0247] The ultrasound transducer just described is combined with theoverall device assembly according to the present embodiment as follows.In assembly, the transducer (830) desirably is “air-backed” to producemore energy and to enhance energy distribution uniformity, as known inthe art. In other words, the inner member (803) does not contact anappreciable amount of the inner surface of transducer inner tubularmember (834). This is because the piezoelectric crystal which formscentral layer (832) of ultrasound transducer (830) is adapted toradially contract and expand (or radially “vibrate”) when an alternatingcurrent is applied from a current source and across the outer and innertubular electrodes (833,834) of the crystal via the electrical leads(836,837). This controlled vibration emits the ultrasonic energy whichis adapted to ablate tissue and form a circumferential conduction blockaccording to the present embodiment. Therefore, it is believed thatappreciable levels of contact along the surface of the crystal mayprovide a dampening effect which would diminish the vibration of thecrystal and thus limit the efficiency of ultrasound transmission.

[0248] For this purpose, the transducer (830) seats coaxial about theinner member (803) and is supported about the inner member (803) in amanner providing a gap between the inner member (803) and the transducerinner tubular member (834). That is, the inner tubular member (834)forms an interior bore (835) which loosely receives the inner member(803). Any of a variety of structures can be used to support thetransducer (830) about the inner member (803). For instance, spacers orsplines can be used to coaxially position the transducer (830) about theinner member (803) while leaving a generally annular space between thesecomponents. In the alternative, other conventional and known approachesto support the transducer can also be used. For instance, O-rings thatcircumscribe the inner member (803) and lie between the inner member(803) and the transducer (830) can support the transducer (830) in amanner similar to that illustrated in U.S. Pat. Nos. 5,606,974;5,620,479; and 5,606,974.

[0249] In the illustrated embodiment, a stand-off (838) is provided inorder to ensure that the transducer (830) has a radial separation fromthe inner member (803) to form a gap filled with air and/or other fluid.In one preferred mode shown in FIG. 16C, stand-off (838) is a tubularmember with a plurality of circumferentially spaced outer splines (839)which hold the majority of the transducer inner surface away from thesurface of the stand-off between the splines, thereby minimizingdampening affects from the coupling of the transducer to the catheter.The tubular member which forms a stand-off such as stand-off (838) inthe FIG. 16D embodiment may also provide its inner bore as the guidewirelumen in the region of the ultrasound transducer, in the alternative toproviding a separate stand-off coaxially over another tubular memberwhich forms the inner member, such as according to the FIG. 16Dembodiment.

[0250] In a further mode, the elongate body (802) can also includeadditional lumens which lie either side by side to or coaxial with theguidewire lumen (804) and which terminate at ports located within thespace between the inner member (803) and the transducer (830). A coolingmedium can circulate through space defined by the stand-off (838)between the inner member (803) and the transducer (830) via theseadditional lumens. By way of example, carbon dioxide gas, circulated ata rate of 5 liters per minute, can be used as a suitable cooling mediumto maintain the transducer at a lower operating temperature. It isbelieved that such thermal cooling would allow more acoustic power totransmit to the targeted tissue without degradation of the transducermaterial.

[0251] The transducer (830) desirably is electrically and mechanicallyisolated from the interior of the balloon (820). Again, any of a varietyof coatings, sheaths, sealants, tubings and the like may be suitable forthis purpose, such as those described in U.S. Pat. Nos. 5,620,479 and5,606,974. In the illustrated embodiment, as best illustrated in FIG.16C, a conventional, flexible, acoustically compatible, and medicalgrade epoxy (842) is applied over the transducer (830). The epoxy (842)may be, for example, Epotek 301, Epotek 310, which is availablecommercially from Epoxy Technology, or Tracon FDA-8. In addition, aconventional sealant, such as, for example, General Electric Silicone IIgasket glue and sealant, desirably is applied at the proximal and distalends of the transducer (830) around the exposed portions of the innermember (803), wires (836, 837) and stand-off (838) to seal the spacebetween the transducer (830) and the inner member (803) at theselocations.

[0252] An ultra thin-walled polyester heat shrink tubing (844) or thelike then seals the epoxy coated transducer. Alternatively, the epoxycovered transducer (830), inner member (803) and stand-off (838) can beinstead inserted into a tight thin wall rubber or plastic tubing madefrom a material such as Teflon®, polyethylene, polyurethane, silastic orthe like. The tubing desirably has a thickness of 0.0005 to 0.003inches.

[0253] When assembling the ablation device assembly, additional epoxy isinjected into the tubing after the tubing is placed over the epoxycoated transducer (830). As the tube shrinks, excess epoxy flows out anda thin layer of epoxy remains between the transducer and the heat shrinktubing (844). These layers (842, 844) protect the transducer surface,help acoustically match the transducer (830) to the load, makes theablation device more robust, and ensures air-tight integrity of the airbacking.

[0254] Although not illustrated in FIG. 16A in order to simplify thedrawing, the tubing (844) extends beyond the ends of transducer (830)and surrounds a portion of the inner member (803) on either side of thetransducer (830). A filler (not shown) can also be used to support theends of the tubing (844). Suitable fillers include flexible materialssuch as, for example, but without limitation, epoxy, Teflon® tape andthe like.

[0255] The ultrasonic actuator (840) generates alternating current topower the transducer (830). The ultrasonic actuator (840) drives thetransducer (830) at frequencies within the range of about 5 to about 20MHz, and preferably for the illustrated application within the range ofabout 7 MHz to about 10 MHz. In addition, the ultrasonic driver canmodulate the driving frequencies and/or vary power in order to smooth orunify the produced collimated ultrasonic beam. For instance, thefunction generator of the ultrasonic actuator (840) can drive thetransducer at frequencies within the range of 6.8 MHz and 7.2 MHz bycontinuously or discretely sweeping between these frequencies.

[0256] The ultrasound transducer (830) of the present embodimentsonically couples with the outer skin of the balloon (820) in a mannerwhich forms a circumferential conduction block in a pulmonary vein asfollows. Initially, the ultrasound transducer is believed to emit itsenergy in a circumferential pattern which is highly collimated along thetransducer's length relative to its longitudinal axis L (see FIG. 16D).The circumferential band therefore maintains its width andcircumferential pattern over an appreciable range of diameters away fromthe source at the transducer. Also, the balloon is preferably inflatedwith fluid which is relatively ultrasonically transparent, such as, forexample, degassed water. Therefore, by actuating the transducer (830)while the balloon (820) is inflated, the circumferential band of energyis allowed to translate through the inflation fluid and ultimatelysonically couple with a circumferential band of balloon skin whichcircumscribes the balloon (820). Moreover, the circumferential band ofballoon skin material may also be further engaged along acircumferential path of tissue which circumscribes the balloon, such as,for example, if the balloon is inflated within and engages a pulmonaryvein wall, ostium, or region of atrial wall. Accordingly, where theballoon is constructed of a relatively ultrasonically transparentmaterial, the circumferential band of ultrasound energy is allowed topass through the balloon skin and into the engaged circumferential pathof tissue such that the circumferential path of tissue is ablated.

[0257] Further to the transducer-balloon relationship just described,the energy is coupled to the tissue largely via the inflation fluid andballoon skin. It is believed that, for in vivo uses, the efficiency ofenergy coupling to the tissue, and therefore ablation efficiency, maysignificantly diminish in circumstances where there is poor contact andconforming interface between the balloon skin and the tissue.Accordingly, it is contemplated that several different balloon types maybe provided for ablating different tissue structures so that aparticular shape may be chosen for a particular region of tissue to beablated.

[0258] In one particular balloon-transducer combination shown in FIG.16A and also in FIG. 18A, the ultrasound transducer preferably has alength such that the ultrasonically coupled band of the balloon skin,having a similar length d according to the collimated ultrasound signal,is shorter than the working length D of the balloon. According to thisaspect of the relationship, the transducer is adapted as acircumferential ablation member which is coupled to the balloon to forman ablation element along a circumferential band of the balloon,therefore forming a circumferential ablation element band whichcircumscribes the balloon. Preferably, the transducer has a length whichis less than two-thirds the working length of the balloon, and morepreferably is less than one-half the working length of the balloon. Bysizing the ultrasonic transducer length d smaller than the workinglength D of the balloon (820)—and hence shorter than a longitudinallength of the engagement area between the balloon (820) and the wall ofthe body space (e.g., pulmonary vein ostium)—and by generally centeringthe transducer (830) within the balloon's working length D, thetransducer (830) operates in a field isolated from the blood pool. Agenerally equatorial position of the transducer (830) relative to theends of the balloon's working length also assists in the isolation ofthe transducer (830) from the blood pool. It is believed that thetransducer placement according to this arrangement may be preventativeof thrombus formation which might otherwise occur at a lesion sight,particularly in the left atrium.

[0259] The ultrasound transducer described in various levels of detailabove has been observed to provide a suitable degree of radiopacity forlocating the energy source at a desired location for ablating theconductive block. However, it is further contemplated that the elongatebody (802) may include an additional radiopaque marker or markers (notshown) to identify the location of the ultrasonic transducer (830) inorder to facilitate placement of the transducer at a selected ablationregion of a pulmonary vein via X-ray visualization. The radiopaquemarker is opaque under X-ray, and can be constructed, for example, of aradiopaque metal such as gold, platinum, or tungsten, or can comprise aradiopaque plastic (e.g., polymer) such as a metal loaded polymer. Theradiopaque marker is positioned coaxially over an inner tubular member(803), in a manner similar to that described in connection with theembodiment of FIG. 13.

[0260] The present circumferential ablation device is introduced into apulmonary vein of the left atrium in a manner similar to that describedabove. Once properly positioned within the pulmonary vein or veinostium, the pressurized fluid source inflates the balloon (820) toengage the lumenal surface of the pulmonary vein ostium. Once properlypositioned, the ultrasonic driver (840) is energized to drive thetransducer (830). It is believed that by driving the ultrasonictransducer 830 at 20 acoustical watts at an operating frequency of 7megahertz, that a sufficiently sized lesion can be formedcircumferentially about the pulmonary vein ostium in a relatively shortperiod of time (e.g., 1 to 2 minutes or less). It is also contemplatedthat the control level of energy can be delivered, then tested forlesion formation with a test stimulus in the pulmonary vein, either froman electrode provided at the tip area of the ultrasonic catheter or on aseparate device such as a guidewire through the ultrasonic catheter.Therefore, the procedure may involve ablation at a first energy level intime, then check for the effective conductive block provided by theresulting lesion, and then subsequent ablations and testing until acomplete conductive block is formed. In the alternative, thecircumferential ablation device may also include feedback control, forexample, if thermocouples are provided at the circumferential elementformed along the balloon outer surface. Monitoring temperature at thislocation provides indicia for the progression of the lesion. Thisfeedback feature may be used in addition to or in the alternative to themulti-step procedure described above.

[0261] FIGS. 17A-C show various alternative designs for the purpose ofillustrating the relationship between the ultrasound transducer andballoon of the assemblies just described above. More specifically, FIG.17A shows the balloon (820) having “straight” configuration with aworking length L and a relatively constant diameter X between proximaland distal tapers (824, 826). As is shown in FIG. 17A, this variation isbelieved to be particularly well adapted for use in forming acircumferential conduction block along a circumferential path of tissuewhich circumscribes and transects a pulmonary vein wall. However, unlessthe balloon is constructed of a material having a high degree ofcompliance and conformability, this shape may provide for gaps incontact between the desired circumferential band of tissue and thecircumferential band of the balloon skin along the working length of theballoon (820).

[0262] The balloon (820) in FIG. 17A is also concentrically positionedrelative to the longitudinal axis of the elongate body (802). It isunderstood, however, that the balloon can be asymmetrically positionedon the elongate body, and that the ablation device can include more thanone balloon.

[0263]FIG. 17B shows another circumferential ablation device assemblyfor pulmonary vein isolation, although this assembly includes a balloon(820) which has a tapered outer diameter from a proximal outer diameterX₂ to a smaller distal outer diameter X₁. (Like reference numerals havebeen used in each of these embodiments in order to identify generallycommon elements between the embodiments.) According to this mode, thistapered shape is believed to conform well to other tapering regions ofspace, and may also be particularly beneficial for use in engaging andablating circumferential paths of tissue along a pulmonary vein ostium.

[0264]FIG. 17C further shows a similar shape for the balloon as thatjust illustrated by reference to FIG. 17B, except that the FIG. 17Cembodiment further includes a balloon (820) and includes a bulbousproximal end (846). In the illustrated embodiment, the proximate bulbousend (846) of the central region (822) gives the balloon (820) a“pear”-shape. More specifically, a contoured surface (848) is positionedalong the tapered working length L and between proximal shoulder (824)and the smaller distal shoulder (826) of balloon (820). As is suggestedby view of FIG. 17C, this pear shaped embodiment is believed to bebeneficial for forming the circumferential conduction block along acircumferential path of atrial wall tissue which surrounds and perhapsincludes the pulmonary vein ostium. For example, the device shown inFIG. 17C is believed to be suited to form a similar lesion to that shownat circumferential lesion (850) in FIG. 17D. Circumferential lesion(850) electrically isolates the respective pulmonary vein (852) from asubstantial portion of the left atrial wall. The device shown in FIG.17C is also believed to be suited to form an elongate lesion whichextends along a substantial portion of the pulmonary vein ostium (854),e.g., between the proximal edge of the illustrated lesion (850) and thedashed line (856) which schematically marks a distal edge of such anexemplifying elongate lesion (850).

[0265] As mentioned above, the transducer (830) can be formed of anarray of multiple transducer elements that are arranged in series andcoaxial. The transducer can also be formed to have a plurality oflongitudinal sectors. These modes of the transducer have particularutility in connection with the tapering balloon designs illustrated inFIGS. 17B and 17C. In these cases, because of the differing distancesalong the length of the transducer between the transducer and thetargeted tissue, it is believed that a non-uniform heating depth couldoccur if the transducer were driven at a constant power. In order touniformly heat the targeted tissue along the length of the transducerassembly, more power may therefore be required at the proximal end thanat the distal end because power falls off as 1/radius from a source(i.e., from the transducer) in water. Moreover, if the transducer (830)is operating in an attenuating fluid, then the desired power level mayneed to account for the attenuation caused by the fluid. The region ofsmaller balloon diameter near the distal end thus requires lesstransducer power output than the region of larger balloon diameter nearthe proximal end. Further to this premise, in a more specific embodimenttransducer elements or sectors, which are individually powered, can beprovided and produce a tapering ultrasound power deposition. That is,the proximal transducer element or sector can be driven at a higherpower level than the distal transducer element or sector so as toenhance the uniformity of heating when the transducer lies skewedrelative to the target site.

[0266] The circumferential ablation device (800) can also includeadditional mechanisms to control the depth of heating. For instance, theelongate body (802) can include an additional lumen which is arranged onthe body so as to circulate the inflation fluid through a closed system.A heat exchanger can remove heat from the inflation fluid and the flowrate through the closed system can be controlled to regulate thetemperature of the inflation fluid. The cooled inflation fluid withinthe balloon (820) can thus act as a heat sink to conduct away some ofthe heat from the targeted tissue and maintain the tissue below adesired temperature (e.g., 90 decrees C), and thereby increase the depthof heating. That is, by maintaining the temperature of the tissue at theballoon/tissue interface below a desired temperature, more power can bedeposited in the tissue for greater penetration. Conversely, the fluidcan be allowed to warm. This use of this feature and the temperature ofthe inflation fluid can be varied from procedure to procedure, as wellas during a particular procedure, in order to tailor the degree ofablation to a given application or patient.

[0267] The depth of heating can also be controlled by selecting theinflation material to have certain absorption characteristics. Forexample, by selecting an inflation material with higher absorption thanwater, less energy will reach the balloon wall, thereby limiting thermalpenetration into the tissue. It is believed that the following fluidsmay be suitable for this application: vegetable oil, silicone oil andthe like.

[0268] Uniform heating can also be enhanced by rotating the transducerwithin the balloon. For this purpose, the transducer (830) may bemounted on a torquable member which is movably engaged within a lumenthat is formed by the elongate body (802).

[0269] Another aspect of the balloon-transducer relationship of thepresent embodiment is also illustrated by reference to FIGS. 18A-B. Ingeneral as to the variations embodied by those figures, thecircumferential ultrasound energy signal is modified at the ballooncoupling level such that a third order of control is provided for thetissue lesion pattern (the first order of control is the transducerproperties affecting signal emission, such as length, width, shape ofthe transducer crystal; the second order of control for tissue lesionpattern is the balloon shape, per above by reference to FIGS. 17A-C).

[0270] More particularly, FIG. 18A shows balloon (820) to include afilter (860) which has a predetermined pattern along the balloon surfaceand which is adapted to shield tissue from the ultrasound signal, forexample, by either absorbing or reflecting the ultrasound signal. In theparticular variation shown in FIG. 18A, the filter (860) is patterned sothat the energy band which is passed through the balloon wall issubstantially more narrow than the band which emits from the transducer(830) internally of the balloon (820). The filter (860) can beconstructed, for example, by coating the balloon (820) with anultrasonically reflective material, such as with a metal, or with anultrasonically absorbent material, such as with a polyurethaneelastomer. Or, the filter (860) can be formed by varying the balloon'swall thickness such that a circumferential band (862), which is narrowin the longitudinal direction as compared to the length of the balloon,is also thinner (in a radial direction) than the surrounding regions,thereby preferentially allowing signals to pass through the band (862).The thicker walls of the balloon (820) on either side of the band (862)inhibit propagation of the ultrasonic energy through the balloon skin atthese locations.

[0271] For various reasons, the “narrow pass filter” embodiment of FIG.19A may be particularly well suited for use in forming circumferentialconduction blocks in left atrial wall and pulmonary vein tissues. It isbelieved that the efficiency of ultrasound transmission from apiezoelectric transducer is limited by the length of the transducer,which limitations are further believed to be a function of thewavelength of the emitted signal. Thus, for some applications atransducer (830) may be required to be longer than the length which isdesired for the lesion to be formed. Many procedures intending to formconduction blocks in the left atrium or pulmonary veins, such as, forexample, less-invasive “maze”-type procedures, require only enoughlesion width to create a functional electrical block and to electricallyisolate a tissue region. In addition, limiting the amount of damageformed along an atrial wall, even in a controlled ablation procedure,pervades as a general concern. However, a transducer that is necessaryto form that block, or which may be desirable for other reasons, mayrequire a length which is much longer and may create lesions which aremuch wider than is functionally required for the block. A “narrow pass”filter along the balloon provides one solution to such competinginterests.

[0272]FIG. 18B shows another variation of the balloon-transducerrelationship in an ultrasound ablation assembly. Unlike the variationshown in FIG. 19A, FIG. 18B shows placement of an ultrasonicallyabsorbent band (864) along balloon (820) and directly in the centralregion of the emitted energy signal from transducer (830). According tothis variation, the ultrasonically absorbent band (864) is adapted toheat to a significant temperature rise when sonically coupled to thetransducer via the ultrasound signal. It is believed that some ablationmethods may benefit from combining ultrasound/thermal conduction modesof ablation in a targeted circumferential band of tissue. In anotheraspect of this variation, ultrasonically absorbent band (864) mayoperate as an energy sink as an aid to control the extent of ablation toa less traumatic and invasive level than would be reached by allowingthe raw ultrasound energy to couple directly to the tissue. In otherwords, by heating the absorbent band (864) the signal is diminished to alevel that might have a more controlled depth of tissue ablation.Further to this aspect, absorbent band (864) may therefore also have awidth which is more commensurate with the length of the transducer, asis shown in an alternative mode in shadow at absorbent band (864).

[0273] In each of the embodiments illustrated in FIGS. 16A through 18B,the ultrasonic transducer had an annular shape so as to emit ultrasonicenergy around the entire circumference of the balloon. The presentcircumferential ablation device, however, can emit a collimated beam ofultrasonic energy in a specific angular exposure. For instance, as seenin FIG. 19A, the transducer can be configured to have only a singleactive sector (e.g., 180° exposure). The transducer can also have aplanar shape. By rotating the elongate body (802), the transducer (830)can be swept through 360° in order to form a circumferential ablation.For this purpose, the transducer (830) may be mounted on a torquablemember (803), in the manner described above.

[0274]FIG. 19B illustrates another type of ultrasonic transducer whichcan be mounted to a torquable member (803) within the balloon (820). Thetransducer (830) is formed by curvilinear section and is mounted on theinner member (803) with its concave surface facing in a radially outwarddirection. The inner member (803) desirably is formed with recess thatsubstantially matches a portion of the concave surface of the transducer(830). The inner member (803) also includes longitudinal ridges on theedges of the recess that support the transducer above the inner membersuch that an air gap is formed between the transducer and the innermember. In this manner, the transducer is “air-backed.” This spaced issealed and closed in the manner described above in connection with theembodiment of FIGS. 16A-E.

[0275] The inverted transducer section produces a highly directionalbeam pattern. By sweeping the transducer through 360° of rotation, asdescribed above, a circumferential lesion can be formed while using lesspower than would be required with a planar or tubular transducer.

[0276] Further catheter constructions and associated methods ofmanufacture are provided in accordance with the present disclosure formounting an ultrasound transducer, as described in FIGS. 16A-E, onto acatheter shaft. Each of the following transducer mounting constructionscan be used with overall catheter construction described above.Accordingly, the following descriptions of an isolated ultrasoundtransducer mounted on an inner section of a catheter shaft will beunderstood to be in the context of the catheter assembly, including anassociated anchoring device (e.g., a balloon), as described above.

[0277] Support Structure for Ultrasonic Transducers

[0278] In order to minimize the transducer damping associated with thesupport structure, the mounting arrangements illustrated in FIGS. 20Athrough 25B support the transducer through attachment to the innermember at locations that are proximal and distal of the ultrasoundtransducer. These designs also capture air within the mountingstructures to air back the transducer. That is, the disclosed modes ofsuspension illustrated in FIGS. 20A through 25B maintain an air gap. Asdiscussed above, air backing of a cylindrical acoustic transducer isdesirable because it provides excellent radial propagation of theultrasound waves. Conversely, the transducer output is damped wheneverit is in contact with any sort of mounting means between the back orinner side of the transducer and the catheter shaft, even highlyelastomeric ones. Therefore, the disclosed designs illustrated in thesefigures are constructed to minimize such damping. To help achieve thisefficiency, the air space between the transducer and the inner member issealed to prevent infiltration by fluids, such as, for example, blood orother fluids. These features are common to the following constructionvariations.

[0279] In each of the variations disclosed below, the transducer isconstructed for use in forming a circumferential lesion at a base of orin a pulmonary vein to treat atrial fibrillation as described above. Inthis application, the transducer preferably is driven in a range ofabout 6 to about 12 MHz. The transducer for this purpose preferably hasa thickness in the range of about 0.009 (0.23 mm) to about 0.013 inches(0.33 mm). A preferred transducer in accordance with the suspendedcoaxial transducer embodiment may have an inner diameter of 0.070 inch(1.8 mm) and an outer diameter of 0.096 inch (2.4 mm); thus, having athickness of 0.013 inch (0.3 mm).

[0280] While the disclosed catheter assemblies and associated methods ofmanufacture for constructing a suspended, generally coaxial ultrasonictransducer have applications in connection with forming circumferentiallesions as described above, those skilled in the art will appreciatethat the present constructions and methods of manufacture also havenumerous other applications. For example, the present constructions andmethods of manufacture can be used for constructing ultrasonic elementsfor the delivery into and the ablation of other body spaces in thetreatment of other medical conditions, as well as in connection withother applications outside of the medical field.

[0281] In another application, the ultrasound ablation device describedabove and the variations thereof described below may also be used forjoining adjacent linear lesions in a less-invasive “maze”-typeprocedure. In yet another application, the devices may be used withinthe coronary sinus to ablate the atrioventricular (AV) node to treatWolff-Parkinson-White syndrome and any other accessory conductivepathway abnormality. In this latter application, it may be desirable toablate only a portion of the circumference of the coronary sinus, and assuch, the ultrasonic ablation devices illustrated in FIGS. 19A and 19Bmay find particular applicability.

[0282] In addition, these types of ablation devices can be mounted ontoa pre-shaped catheter shaft that has a curvature that generally matchesa natural curvature of the coronary sinus about the exterior of theheart. Such pre-shaped catheter may self-orient within the coronarysinus to position the active ultrasonic transducer toward the inner sideof the coronary sinus (i.e., toward the interior of the heart) so as todirect transmission toward the AV node. A catheter constructed with theultrasonic transducer mounting assemblies disclosed herein can also bedesigned without an anchoring balloon for use on an end of a flexiblecatheter for the treatment of ventricular tachycardia.

[0283] Referring now to FIGS. 20A and 20B, an external layer coupled tothe transducer with a coupling adhesive is described below. Bysuspending the transducer from such an external protective layer, theproblem of maintaining a minimally damped internal mounting scheme isresolved. As illustrated in FIGS. 20A and 20B, a guide member trackingmember (900) has a central guide member lumen (902) for slidablyengaging and tracking over a guide member (e.g., a guidewire or asteerable catheter). The transducer (904) is generally coaxiallydisposed over the tracking member (900); however, it is understood thatthe transducer (904) can be asymmetrically positioned relative to anaxis of the guide member tracking member (900) provided an air gapexists between the transducer inner surface and the tracking member(900). An air space (906) exists between the transducer (904) and thetracking member (900), thereby providing an air-backing to maximize theoutward radiation of the ultrasonic energy, as described above. It isunderstood that the transducer need not be mounted on a portion of thecatheter that tracks over a guide member, but rather can be mounted on adistal end of a steerable catheter or can be arranged in a side-by-siderelationship with such guide member.

[0284] The transducer (904) is held suspended over the tracking member(900) by the cooperative arrangement of an outer cover (910), forexample, a shrink-wrap polymeric material (e.g., PET), and end plugs(912) bonded to a length of the tracking member (900) proximal anddistal to the transducer (904). In the embodiment illustrated in FIGS.20A and 20B, the end plugs (912) are formed of adhesive and lie underthe cover (910), and a layer of adhesive (908) covers the transducer(904) and couples the transducer (904) to an inner surface of the outercover (910).

[0285] The proper air gap may be ensured during setting of the adhesiveend plugs (912) by inserting three or more beading mandrels between thetracking member and the transducer. These mandrels would preferably beevenly distributed radially about the tracking member (900) and wouldrun axially along the length of the transducer (910). The beadingmandrels can be sized so as to create a desired air gap (e.g., 0.005inches (0.13 mm)). Since the mandrels must be removed, it is preferredthat the beading mandrels be made out of a material to which the epoxyadhesive will not stick, such as for example, metal or silicone, andextend beyond one end of the transducer (904) during the assemblyprocess. FIG. 20B is a cross-sectional view through the transducer alongline B-B of FIG. 20A. The thickness of the adhesive layer can be in therange of about 0.0005 (0.013 mm) to about 0.001 inches (0.025 mm). Thecover can have a thickness in the range of about 0.001 to about 0.003inches.

[0286]FIGS. 21A and 21B illustrate another embodiment of the suspendedcoaxial transducer of the present invention. With reference to FIG. 21A,the transducer (904) is shown in perspective view formed inside anenclosure such as a thin shell or housing, which has mounting flanges(914) extending proximally and distally from the transducer. FIG. 21Bshows the transducer in transverse section. The transducer (904) issuspended over the tracking member (900) by the mounting flanges (914)which extend from either end of the transducer (904). An air space (906)exists between the inner surface of the housing (920) that encapsulatesthe transducer (904) and the tracking member (900). The air space (906)extends to and may be more pronounced in the regions between themounting flanges (914) and the tracking member (900), depending on theconfiguration of the mounting flanges.

[0287] The mounting flanges (914) may be formed in a variety ofconfigurations, as long as they extend axially from the transducer andare capable of mounting to the tracking member (900) so as to suspendthe transducer over the tracking member (900). For example, the flanges(914) may be centrally disposed and of a smaller outer diameter than thecoated transducer, as illustrated in FIGS. 21A and 21B. Alternatively,the flanges may be of the same diameters or may have a larger innerdiameter than the coated transducer. The flanges may also be disposedasymmetrically, for instance, extending from the top or bottom surfacesof the transducer. With respect to the method of constructing suchsupport assemblies as herein shown and described by reference to thespecific embodiments, the shapes provided may be imparted onto astarting “plug” or workpiece of material, such as by grinding or heatprocessing, or the support may be molded, laminated, cast, or otherwiseformed as a “composite” of sorts wherein each region of the support is asubassembly that is connected to the others to form the supportstructure.

[0288] The mounting flanges (914) may also be mounted in a variety ofstructures (916) attached to the delivery member (900) on the proximaland distal sides of the transducer. One variation in the mountingstructure (916) can be an end cap with a groove sized to receive themounting flange, as shown in FIG. 21B. Such end cap can be made of asuitable plastic or elastomer (e.g., silicone, PET, etc.). Anothervariation of the mounting design is illustrated in FIG. 22, which showsa support sleeve and shrink-wrap cover. In this variation, thetransducer (904) with molded coating (920) and flanges (914) issuspended over the tracking member (900) by a support sleeve (928) uponwhich the flanges (914) rest. The support sleeve (928) may have a groovefor engaging the flange as shown. The transducer (904) can be secured byheat shrinking a covering sleeve (926) (e.g., PET) over the flanges(914), thereby maintaining the air gap (906) between the transducer(904) and the tracking member (900)—such resulting construction alsobeneficially provides a seal to prevent fluid from infiltrating into theairspace under the transducer. The mechanical joints formed bycompressing the ends of the mounting flanges between the support sleeve(928) and the covering sleeve (926) supports the ends of the mountingflanges (914) with the transducer suspended between the resultingproximal and distal joints.

[0289] In accordance with another variation, as illustrated in FIG. 23,the mounting structure can include O-rings (922), upon which the flanges(914) rest, thereby suspending the transducer (904) above the trackingmember (900), wherein the proximal flange is bonded with adhesive (924),preferably a flexible adhesive, to the tracking member proximal to theproximal O-ring and the distal flange is bonded with adhesive to thetracking member distal to the distal O-ring. Moreover, thetransducer/housing assembly and flanges thus mounted by adhesive may befurther secured by heat shrinking a plastic (e.g., polymeric) coveringsleeve (926) over the flange (914). The shrink-wrap cover could be fusedto the elastomeric adhesive (924) by heat or chemical process. In avariation, the entire suspended coaxial transducer assembly, includingthe flanges (914) could be covered with the shrink-wrap material (926)that is also bound by the adhesive. The assembly can also be dippedcoated to form the outer covering.

[0290] The O-ring mounting variation has the advantage of preventingadhesive from running into the air gap, for example, when the assemblyis heated in applying the shrink-wrap. Also, the elastic properties ofthe O-ring tend to push the flange tightly against the shrink-wrap outercover. The O-rings also support the transducer about the tracking memberduring the assembly process (e.g., when applying the epoxy and heatshrinking) to hold the transducer in a generally concentric positionrelative to an axis of the tracking member (900) before the assemblycures.

[0291] The thin molded shell (920) that coats the transducer (904) andforms the flanges (914) is preferably made of a high temperatureresistant elastomer, an in any event a material that may withstandtemperatures up to about 200° C. in the event the transducer is run athigh power, such as at a power sufficient to ablate circumferentialregions of tissue. The material may be a thermoset elastomer, such asurethane or silicone rubber. Alternatively, the material could be athermoplastic polymer, such as polyurethane, PET, or any other polymericthermoplastic known to those of skill in the art for manufacture ofmedical devices. The shell should have a Shore hardness of about 90(scale A). However, the greater the unsupported distance along theflange between the mounting structure (e.g., the end cap, support sleeveor O-ring) and the transducer, the greater the flexibility of theflange. While high flexibility of the flanges is desirable for dampingprevention, the stiffness of the flange material must nevertheless besufficient to prevent the suspended transducer from bowing andcontacting the tracking member. The stiffness can be increased by usinga material of higher Shore hardness (e.g., a thermoplastic rather thansilicone rubber) and/or by increasing the thickness of the flange.

[0292] Several methods of manufacturing the transducer with a thincoating of plastic or rubber (e.g., silicone or other elastomericcoatings) and axial flanges are disclosed herein. First, the housingcould be injection molded about the transducer. The injection moldingcould be accomplished in at least two separate stages. Using silicone asan exemplifying material, a base layer of silicone is placed beneath thetransducer and axially to form the flanges, while the transducer ismounted on a base sleeve of silicone on a mandrel. When cured, themandrel is removed, leaving the transducer coated on its upper surfacewith the silicone support cover the inner surfaces of the transducer.The outer coating and the inner sleeve of silicone desirably are joined,either by a fusion of the materials during the injection process or byheat or chemical processes, or by other means well known in the art. Ifan inner support is not used, the bottom surfaces next can be injectionmolded in similar manner. The two half molds can then be joined by heator chemical process to form the complete shell. Instead of injectionmolding the second surface of the transducer, the half-coated transducercould be formed by dipping in a liquid elastomer, one or several times.Since the flange would be difficult to form by dipping, it would bepreferred that the flange be injection molded. Alternatively, it may bedesirable to use a transducer coated only on one surface (e.g., theinner surface). Lastly, the transducer coated with a thin shell may bemade by dipping the transducer one or several times to achieve thedesired thickness. A mandrel may be used to hold the transducer duringthe dipping process.

[0293] Another variation of the suspended coaxial transducer (904) isillustrated in FIG. 24 having injection molded end mounts (930). In thisvariation, the transducer is suspended over the tracking member (900) byfitting within grooves formed in injection molded end mounts (930). Thegrooves may be molded or formed during post-molding processing. The endmounts are molded to have an inside diameter of close to that of theoutside diameter of the tracking member (900) so as to facilitatefastening to the tracking member (900) by adhesive or other meansproximal and distal to the transducer. The end mounts also have anincreased diameter in the mounting region, so as to engage thetransducer within the mounting grooves at a fixed distance above thetracking member (900), thereby creating the desired air gap (906). Thetransducer may be secured within the end mount grooves by adhesive,fasteners, etc.

[0294] A mounting balloon variation of the suspended coaxial transduceris shown in FIG. 25A. In this variation, the transducer (904) is mountedon an expandable member or balloon (932) that creates a flexiblemounting structure and an air gap (906) between the balloon (932) andthe outer surface of the tracking member (900). The transducer (904) canbe sealed to the balloon by elastomeric adhesive. In this variation, theelectrical lead (933) to the inner conductive layer of the ultrasoundtransducer may be sealed using elastomeric adhesive between the balloon(932) and the inner layer of the transducer (904). In another variation,the adhesive can be conductive (e.g., contain silver) and a surface ofthe balloon can be coated with or formed by a conductive layer so as toprovide an electrical path from a lead in contact with or embeddedwithin the adhesive, through the conductive layer an to an innerelectrode of the transducer to power the inner electrode.

[0295] With reference to FIG. 25B, there is shown a perspective view ofone possible sequence of making the balloon mounted transducer. On theleft side, a tubular balloon stock (932) is shown before inflation,having a layer of adhesive (934) applied to the outer surface. In thecenter, the transducer (904) is shown with the inner lead (933) inplace. Next, the transducer (904) is inserted over the balloon (932).The distal region of the balloon is then closed and pressurized air orfluid is applied at the proximal end causing the balloon to inflate andpress radially outward against the inner surface of the transducer.During this process, the balloon may be “cold blown” without thepresence of heat as known in the art, or can be heated. In this latterprocess, the balloon is inflated while heating the balloon material to aglass transition temperature within a “capture tube.” The capture tubedesirably has a diameter generally equal to an inner diameter of thetransducer so that the formed balloon will have an outer diameterapproximating the inner diameter of the transducer. In addition, thecapture tube can be configured so as to produce a desired profile forneck sections of the balloon on either side of a central section onwhich the transducer will be mounted. In either a cold or heatedprocess, the balloon is inflated to a size causing the adhesive to bondthe interior surface of transducer against an exterior section of theballoon.

[0296] The adhesive bonds the outer surface of the balloon to the innersurface of the transducer; the bonding step may require heating. Inheating process, the adhesive desirably can withstand the blowingtemperatures, as one skilled in the art will readily appreciate. Theinner lead is thereby fixed in contact with the inner surface of thetransducer and exits through the adhesive seal between the balloon andthe transducer.

[0297] The mounting construction illustrated in FIG. 25A can also bemade by performing the balloon (either by a cold or heated blowingprocess) and subsequently placing the transducer over the inflatedsection of the balloon. Adhesive is placed between the balloon and thetransducer, either by precoating the balloon and/or transducer withadhesive, or by injecting adhesive between the balloon and thetransducer. The preformed balloon may dip coated with an elastomer(e.g., silicone).

[0298] When assembled, the transducer can be cover by an outer jacketingor cover, but need not be. Such coating or jacket can be formed in anyof a variety of ways, including, for example, but without limitation, bya dipping process or by heat-shrinking a cover over the transducer andballoon assembly. The coating or jacket inhibits fluid within theanchoring balloon (822) (FIG. 16A) from seeping between the mountingballoon (932) and the transducer (904).

[0299] The mounting balloon (932) can have a fairly rigid structure andgenerally maintain its shape after the blowing process, or can collapsedown after blowing. When assembled to the tracking member (900) (e.g.,the catheter shaft) the collapse balloon is inflated and pressurized toassume its shape. A static air lock is formed by sealing the ends of themounting balloon in a well known manner.

[0300] The mounting balloon, as apparent from the above description, canbe formed of any of a variety of materials used to form catheterballoon, including those that are compliant and those that arenon-compliant. For instance, a mounting balloon that holds its shape canbe made of a relatively rigid plastic (e.g., a polymer) such as apolyethylene (“PE”; preferably linear low density or high density orblends thereof), polyolefin copolymer (“POC”), polyethylene terepthalate(“PET”), polyimide, PEBAX or a nylon material. A balloon assembled witha static air lock can be made of any of a variety of compliant andnon-compliant materials, such as any of those identified herein.

[0301] While the above mounting constructions have been illustrated withreference to a cylindrical transducer, it is understood that thesemounting constructions can be used with arcuate or flat transducerpanels. Additionally, the transducer or transducer assembly (when formedby a plurality of transducer panels) need not extend entirely about thetracking member. In such a case, as noted above, the catheter may berotated through an arc or completely rotated, depending upon theapplication, to create the desired lesion pattern.

[0302]FIG. 26 illustrates another mounting arrangement for theultrasound transducer (904) on the tracking member (900). Thisvariation, however, does not suspend the transducer (904) from supportsthat attached to the tracking member on proximal and distal sides of thetransducer. Rather, the mounting arrangement includes an elastomericsupport (940) that in interposed between the ends of the transducer(904) and the tracking member (900).

[0303] As seen in FIG. 26, as well as in FIGS. 27, 28A and 28B, thesupport (940) has a generally tubular configuration. The support (940)includes thick walled end portions (942) and a thin walled centralportion (944). The inner diameter of the support (940) generally matchesthe outer diameter of the tracking member (900), and the outer diameterof the end portions (942) generally matches the inner diameter of thetransducer (904). The outer diameter of the central portion (944) issmaller than the outer diameter of the end portions (942) therebycreating an air gap between the transducer (904) and the central portion(944). When assembled, the transducer is attached to the end portions(942) of the support (940) by a suitable adhesive or epoxy.

[0304] FIGS. 29A-29B illustrate a further design according to theinvention wherein a cylindrical ultrasound transducer (1000) is mountedonto the shaft (1052) of a delivery member (1050) via a support member(1020). The support member (1020) has two end regions (1022,1024) and anintermediate region (1026) therebetween. The transducer (1000) coaxiallysurrounds and rests on the intermediate region (1026), whereas the endregions (1022,1024) function as flanges by mounting onto the underlyingshaft (1052) without bridging across the radial separation area (1010)between the outer surface (1055) of the shaft (1052) and the innersurface (1006) of transducer (1000). In addition, each of the endregions (1022,1024) includes an outer lip (1023,1025), respectively,which border the ends (1002,1004) of the transducer (1000), alsorespectively, and provide in one regard for the longitudinal stabilityof the transducer position on the shaft (1052). In one further mode,outer jackets (1030,1040) can be secured over the end regions(1022,1024,) and onto the shaft (1052) such as via adhesive fillets(1036,1046) and thereby effectively seal the radial separation area(1010) from fluid ingress without covering the transducer (1000). Theend regions (1022,1024) of the support member (1020) also include innerlips (1023′,1025′) which rest on the outer surface (1055) of the shaft(1052) outside of the radial separation area (1010) and provide the“stand-offs” to ensure airbacking along radial separation area (1010).

[0305] As elsewhere disclosed herein, the support member (1020)preferably is constructed of an elastomeric or at least flexiblematerial in order to decrease damping, and is also preferably relativelyheat resistant and non-degradable at temperatures around about 200° C.In addition, dimensions for the various features of the support member(1020) include: outer diameter of surface (1055) of the shaft (1052) ofaround about 0.050 inches; inner diameter of the intermediate region(1026) of around about 0.060 inches; and inner diameter of thetransducer (1000) of around about 0.070 inches.

[0306]FIGS. 30A and 30B illustrate a modification wherein a supportmember (1060) is formed from a body (1062) having a first end (1064), asecond end (1066), and a raised portion (1068) disposed between thefirst and second ends (1064,1066). As shown in FIG. 30A, the raisedportion (1068) extends annularly around the body (1062) and forms afirst end annular face (1070) and a second annular face (1072). Thefirst and second annular faces (1070,1072) face towards the first end(1064) and the second end (1066), respectively. The body (1062) ispreferably annular in shape and defines a longitudinal axis (1074).Also, preferably, the annular faces (1070,1072) extend approximatelynormally to the axis (1074). Preferably, the body (1062) is made from arigid material such as polyimide. However, it is conceived that the body(1062) can be formed of any rigid material, including metals such asplatinum, stainless steel, nitenol, or other rigid plastics.

[0307] Still referring to FIG. 30A, the body (1062) extends over alength (1076) between the raised portion (1068) and the first end(1064). Additionally, the body (1062) extends over a length (1078)between the raised portion (1068) and the second end (1066). The length(1078) is less than the distance (1076). Additionally, the raisedportion (1068) has a thickness (1080).

[0308] With reference to FIG. 30B, the transducer (1000), constructed inaccordance with the description of the transducer (1000) disclosed abovewith reference to FIGS. 29A-29D, is supported over the shaft (1052) ofthe delivery member (1050) by two support members (1060,1060′). Thefirst ends (1064, 1064′) of the support members (1060,1060′),respectively, are arranged so as to support the inner surface (1006) ofthe transducer (1000). As such, the portions of the body (1062) havingthe length (1067) are positioned within the transducer (1000) and theportions of the body (1062) having the shorter length (1078) extend awayfrom the transducer (1000) and the annular faces (1072,1072′),respectively.

[0309] The support members (1060,1060′) are preferably bonded to thetransducer (1000) with EP42ET. The EP42ET adhesive is spread so as toform a bond between the first ends (1064,1064′) and the annular faces(1070,1070′), and the transducer (1000). The second ends (1066,1066′)are preferably bonded to the shaft (1052) with loctite 498 (1082). Theloctite (1082) is applied in the form of a fillet to substantially coverthe annular faces (1072,1072′) and the ends (1066,1066′) of the supportmembers (1060,1060′), respectively. Additionally, the adhesive (1072) ispreferably spread to form a fluid-tight seal between the second ends(1066,1066′) and the shaft (1052).

[0310] In the illustrated embodiment, a notch (not shown) is formed inthe support member (1060′) and an electric lead wire (1084) extendsthrough the notch and is connected to the inner surface (1006) of thetransducer (1000). As noted above, the inner surface (1006) of thetransducer (1000) defines one of the electrodes of the transducer(1000). Thus, the electric lead wire (1084) is connected to the innersurface (1006) for powering the transducer (1000). Similarly, a furtherelectric lead wire (not shown) is attached to the outer surface (1002)of the transducer (1000) for powering the transducer (1000).

[0311] As shown in FIG. 30B, the inner ends (1064,1064′) of the supportmembers (1060,1060′) are spaced from each other such that the radialseparation area (1010) is maintained between the inner surface (1006) ofthe transistor (1000) and the shaft (1052). In the illustratedembodiment, the bond between the support members (1060,1060′) and thetransducer (1000) is maintained in a fluid-tight state by the EP42ETadhesive. Additionally, the loctite 498 (1082) maintains a fluid-tightseal between the support members (1060,1060′) and the shaft (1052).

[0312] Referring again to FIG. 30A, an illustrative example of thesupport members (1060,1060′) is dimensioned as follows. An innerdiameter of the body (1062) is 0.058″±0.001″. An outer diameter of thebody (1062) is 0.067″±0.001″. The length (1080) of the raised portion(1068) is approximately 0.015″±0.001″. The length (1078) of the body(1062) between the raised portion (1068) and the second end (1066) ispreferably 0.030″±0.002″.

[0313] The outer diameter of the raised portion (1068) is preferably0.090″±0.002″. The overall length of the support member (1060), i.e.,the sum of the lengths (1076,1080,1078) is preferably 0.095″±0.002″. Theabove-noted dimensions for the support members (1060,1060′) are sizedfor a shaft, such as such the shaft (1062) illustrated in FIG. 30Bhaving an outer diameter of approximately 0.057″.

[0314] It will be understood that the above-noted dimensions are merelyexemplifying of one preferred form. The dimensions each depend upon oneanother, upon the density and shape of the support members, transducer,and the shaft, and the desired normal operating conditions. It isunderstood that one of skill in the art can vary the dimensions to adaptthe catheter for a particular application through routineexperimentation, in view of this disclosure herein.

[0315] With reference to FIG. 30B, the outer surface (1002) of thetransducer (1000) is preferably left exposed. Thus, when the illustratedtransducer (1000) is provided within an expandable balloon (not shown)and a fluid such as saline, or the like, as noted above, is supplied tothe interior of the balloon so as to inflate the balloon for use in atissue ablation procedure, the outer surface (1002) of the transducer(1000) is exposed to the fluid. As noted above, the transducer (1000)preferably is a piezoelectric ultrasonic transducer having one electrodeon its inner surface (1006) and another electrode on its outer surface(1002).

[0316] It has been found that by leaving at least a portion of the outersurface (1002) exposed to the fluid, reflected ultrasonic energy isgreatly lowered during the operation of the transducer (1000).Additionally, since there is less material applied to the outer surface(1002) of the transducer (1000), the delamination of such outer coatingis attenuated, thus, enhancing the useful life of the catheter.

[0317]FIG. 31A illustrates a further modification of the catheterillustrated in FIGS. 29A-29D. As shown in FIG. 31A, the transducer 1000is sealed at its proximal and distal ends by elastic washers (1088,1088′). Additionally, pressure washers (1090, 1090′) are provided on theouter sides of the elastic washers (1088, 1088′), respectively.

[0318] As shown in FIG. 31A, the transducer (1000) includes an outersurface (1002) and an inner surface (1006). The transducer (1000) issuspended by the elastic washers (1088, 1088′) so as to maintain theradial separation (1010) between the inner surface (1006) and the shaft(1052).

[0319] The elastic washers (1088, 1088′) are preferably formed byannular members composed of any appropriate elastic material including,for example, silicone, rubber, or the like. As shown in FIG. 31A, theelastic washers (1088, 1088′) include through holes (1092) defining aninner diameter which provides a close fit to the shaft (1052).

[0320] The pressure washers (1090, 1090′) are preferably formed from amore rigid material, such as, for example, but without limitation,metals such as platinum, stainless steel, PET, and polyimide. Similarlyto the elastic washers (1088, 1088′), the pressure washers (1090, 1090′)include through holes (1094, 1094′) which have an inner diameter sizedto form a close fit with the shaft (1052). Preferably, during assembly ,the pressure washers (1090, 1090′) are pressed against the elasticwashers (1088, 1088′) so as to form a fluid-tight seal against the endsof the transducer (1000). With the pressure washers (1090, 1090′)pressed against the elastic washers (1088, 1088′), the pressure washers(1090, 1090′) are then secured to the shaft (1052) so as to maintain theelastic washers (1088, 1088′) in fluid-tight contact with the transducer(1000).

[0321] Optionally, the elastic washers (1088, 1088′) can also be bondedto the proximal and distal ends of the transducer (1000). The outersides of the elastic washers (1088, 1088′) are likewise bonded to thepressure washers (1090, 1090′) with a suitable adhesive. Finally, anadditional adhesive or sealant is provided at the interface between thethrough holes (1094, 1094′), and the shaft (1052). As such, the radialseparation (1010) is maintained and is sealed to prevent fluid frominfiltrating into the separation (1010). As noted above, with referenceto FIG. 30, the outer surface (1002) of the transducer (1000)illustrated in FIG. 31A is preferably left exposed to a fluid usedduring an ablation process.

[0322]FIG. 31B illustrates a modification of the catheter shown in FIG.31A. As shown in FIG. 31B, a splined support member (1096) supports thetransducer (1000) relative to the shaft (1052) so as to maintain the airgap (1010) between the transducer (1000) and the shaft (1052). Thesplined support member (1096) can be constructed in accordance with thedisclosure of the stand-off (838) set forth above with reference toFIGS. 16A-16D. Sealing washers (1098, 1098′) are placed in sealingengagement with the ends of the transducer (1000). In the illustratedembodiment, adhesive (1099) replaces the pressure washers (1090, 1090′)illustrated in FIG. 31A.

[0323]FIG. 32A illustrates a further modification of the transducerassembly illustrated in FIGS. 29A-29B. As shown in FIG. 32A, thetransducer assembly (1100) includes the transducer (1000) mounted ontothe shaft (1052) via a splined support member (1102). The support member(1102) is preferably in the form of an elastic or an elastomericmaterial, such as silicone, and includes a plurality of splinesextending longitudinally along the support member (1102). Theconstruction of the splines included on the support (1102) can be inaccordance with the construction of the splines (839) included on thestandoff (838) illustrated in FIG. 16C. Thus, a further description ofthe splined support member (1102) is not necessary for one of ordinaryskill in the art to practice the invention as disclosed herein.

[0324] As shown in FIG. 32B, support member (1102) is positioned suchthat the proximal and distal ends (1104, 1106) of the support (1102)terminate within the transducer (1000). The proximal and distal ends(1004, 1002) of the transducer (1000) are sealed to the shaft (1052)with a fillet of silicone or epoxy adhesive (1108). Additionally,jackets (1110, 1112) are formed over the fillets (1108).

[0325] As shown in FIG. 32A, the jackets (1110, 1112) extend completelyover the fillets (1108) and overlap portions of the proximal and distalends (1004, 1002) of the transducer (1000). In the illustratedembodiment, the jackets (1110, 1112) are formed from a rigid materialsuch as PET. In the illustrated embodiment, the jackets (1110, 1112)overlap the proximal and distal ends (1004, 1002) of the transducer(1000) over a distance (1114) of approximately ½ to 1 mm. Additionally,the jackets (1110, 1112) are sized so as to leave at least a portion ofthe outer surface of the transducer (1000) exposed. In the illustratedembodiment, since the transducer (1000) is approximately 6 to 7 mm, theexposed portion of the transducer (1000) extends over a length (1116) ofapproximately 5 millimeters. Additionally, in the illustratedembodiment, the jackets (1110, 1112) are formed from a layer of PEThaving a thickness of approximately 0.001 inches to 0.0005 inches. Asshown in FIG. 32A, epoxy fillets (1117) are preferably provided at theinterface between the inner ends (1119) and the outer surface of thetransducer (1000). As such, the fillets (1117) provide further anchoringeffect of the jackets (1110, 1112) to the outer surface of thetransducer (1000).

[0326] It will be understood that the above-noted dimensions are merelyexemplifying of one preferred form. The dimensions each depend upon oneanother, as well as other characteristics. It is understood that one ofordinary skill in the art can readily vary the dimensions to adapt thecatheter for a particular application through routine experimentation,in view of the disclosure herein.

[0327] With reference to FIG. 32B, an electric lead wire (1118) can beconnected to the outer surface of the catheter (1000). As shown in FIG.32B, a notch (1120) is formed in the jacket (1110) so as to allow thelead wire (1118) to be electrically connected to the outer surface ofthe transducer (1000).

[0328]FIG. 33A illustrates a further modification of the circumferentialablation device assembly (800) illustrated in FIGS. 16A-16D. As shown inFIG. 33, the circumferential ultrasound transducer (830) is supportedcoaxially about an inner member (1122) and is supported about the innermember (1122) in a manner providing a gap between the inner member(1122) and the transducer inner tubular member (834). In the illustratedembodiment, a splined support member (1124) is disposed between theinner tubular member (834) and the inner member (1122) to maintain theair gap therebetween.

[0329] The splined support member (1124) can be constructed inaccordance with the description of the standoff (838) having splines(839) set forth above with reference to FIG. 16C. Thus, a furtherdescription of the splined support member (1124) is not necessary forone of ordinary skill in the art to practice the invention as disclosedherein.

[0330] Similarly to the standoff (838) disclosed above with reference toFIG. 16C, the splined support member (1124) includes a plurality ofcircumferentially spaced outer splines so as to maintain a gap betweenthe inner member (1122) and the inner tubular member (834).Additionally, in the illustrated embodiment, the proximal end (1126) andthe distal end (1128) of the transducer (830) are sealed to the innermember (1122) with fillets of adhesive. Preferably, the fillets (1130,1132) are formed of a silicone adhesive. However, it is apparent to oneof ordinary skill in the art that the adhesive may be any of a varietyof adhesives.

[0331] As shown in FIG. 33A, an outer jacket (1134) is secured over theproximal end (1126) and the sealing bead (1130) and onto the innermember (1122) thereby further sealing the space between the inner tube(834) and the inner member (1122) from the ingress of fluid. In theillustrated embodiment, the jacket (1134) is in the form of ashrink-wrapped layer of PET. However, it is apparent to one of ordinaryskill in the art that the jacket (1134) can be constructed in accordancewith any of the jackets disclosed above. A distal end jacket (1136) cansimilarly be provided on the distal end (1128) of the transducer (830)(FIG. 33B).

[0332] With reference to FIG. 33B, a cooling system (1138) can beincorporated with the transducer assembly illustrated in FIG. 33A. Asshown in FIG. 33B, the cooling system (1138) includes a cooling chamber(1140) defined by an outer wall (1142). In the illustrated embodiment,the outer wall (1142) is formed of a balloon or bag that extends overthe distal and proximal ends (1126, 1128) of the transducer (830).

[0333] As shown in FIG. 33B, the wall (1142) includes a proximal neckportion (1144) and a distal neck portion (1146). Additionally, the innermember (1122) extends from an elongate body (1147). The elongate body(1147) can be constructed in accordance with the elongate body (802)illustrated in FIG. 16A. The proximal neck portion (1144) of the wall(1142) is sealed to the elongate body (1147). Additionally, the distalneck portion (1146) is sealed to a distal guidewire port (1148). Thedistal guidewire port (1148) can be constructed in accordance with thedistal guidewire port (805) disclosed above with reference to FIG. 16A.

[0334] As shown in FIG. 33B, the elongate body (1147) includes a fluiddischarge (1150) positioned distally from the proximate neck portion(1144). Additionally, the inner member (1122) includes a distal port(1152) arranged distally from the transducer (830), but proximally fromthe distal neck portion (1146).

[0335] In operation, when the transducer (830) is driven by a powersource, such as the power source (840) disclosed above with reference toFIG. 16B, a coolant can be supplied through a coolant lumen extendingthrough the elongate body (1147) so as to flow into the cooling chamber(1140) through the proximal coolant port (1150), around the transducer(830) and into the distal coolant port (1152). For example, as shown inFIG. 33B, coolant flows, indicated generally by the arrows CF can enterthe cooling chamber (1140), contact the transducer (830) and flow out ofthe cooling chamber (1140), thereby cooling the transducer (830). In theillustrated embodiment, the outer electrode (833) is at least partiallyexposed to the coolant flows C_(F). Thus, the thermal conduction of heatfrom the transducer (830) to the coolant flow C_(F) is enhanced.

[0336] After the coolant flow C_(F) enters the distal coolant port(1152), the coolant flow can be directed through the guidewire lumen(not shown) and into the patient's body. Alternatively, the coolant flowcan be returned to the proximate end of the elongate body (1147) througha coolant return lumen (not shown).

[0337] With reference to FIG. 33C, the cooling assembly (1138) isillustrated as being provided within an expandable balloon (1154). Theexpandable balloon (1154) can be constructed in accordance with thedisclosure of the expandable balloon (820) set forth above withreference to FIGS. 16A and 16C. Thus, a further description of theexpandable balloon (1154) is not necessary for one of ordinary skill inthe art to practice the invention as disclosed herein.

[0338] Although separate lumens can be provided for supplying coolantfluid to the coolant chamber (1140) and for returning coolant fluid tothe proximal end of the elongate body (1147), in the illustratedexample, coolant fluid is supplied to the coolant chamber (1140) via athermocouple lumen (1156). As shown in FIG. 33C, a thermocouple (1158)is placed in operative contact with the outer surface (833) of thetransducer (830) so as to provide temperature data for controlling theoutput of the transducer (830).

[0339] In the illustrated embodiment, the cooling chamber wall (1142) isformed of a PET bag having an inner diameter of 0.110 inches and athickness of 0.0005 inches. However, it is apparent to one of ordinaryskill in the art that these dimensions can be varied according to thedesired characteristics of the cooling chamber (1140).

[0340]FIGS. 34A and 34B illustrate a modification of the embodiment ofFIGS. 20A and 20B. As noted above with respect to FIGS. 20A and 20B, aplurality of mandrels can be inserted between the transducer (904) andthe tracking member (900). With the mandrels arranged around thetracking member (900), a desired air gap can be defined between thetransducer (904) and the tracking member (900). The transducer (904) isthen bonded to the tracking member (900) with an adhesive that will notstick to the material used to form the mandrels. After the transducer(904) has been bonded to the tracking guide member (900), the mandrelsare removed and the transducer (904) is then sealed to the trackingmember (900) with the cover (910).

[0341] In the modification illustrated in FIG. 34A, a plurality ofmandrels (1160) are arranged between the tracking member (900) and ininner surface of the transducer (904). The mandrels (1160) are sized andspaced so as to generate a substantially uniform air space (906) betweenthe transducer (904) and the tracking member (900).

[0342] As shown in FIG. 34B, the mandrels (1160) are preferably sized tobe slightly shorter than the transducer (904). With the mandrelsarranged between the transducer (904) and the tracking member (900), theair space is sealed with an adhesive such as loctite 498 (1162). In theillustrated embodiment, a silicone seal seals the proximal and distalends (1164, 1166) of the transducer (904) against the tracking member(900). Additionally, a loctite fillet (1168, 1170) is formed over thesilicone (1162, 1164).

[0343] In the illustrated embodiment, the tracking member (900) isformed of a polyimide tube having an outer diameter of approximately0.048 inches and the mandrels (1160) are formed of polyimide rods ortubes having an outer diameter of approximately 0.008 inches. However,it is apparent to one of ordinary skill in the art that the above-noteddimensions can be varied according to the desired characteristics andoverall dimensions of the catheter.

[0344]FIG. 35 illustrates a further modification of the embodimentillustrated in FIG. 26. As shown in FIG. 35, a transducer assembly(1170) includes a transducer (1172) mounted to an inner member (1174).The construction of the transducer (1172) can be in accordance with thedisclosure of the transducer (830) disclosed above with reference toFIGS. 16A-16B. Thus, a further description of the transducer (1172) isnot believed to be necessary for one of ordinary skill in the art topractice the invention as disclosed herein.

[0345] In the illustrated embodiment, the transducer (1172) has an outerelectrode (1176) and an inner electrode (1178). The transducer (1172) issupported relative to the inner member (1174) so as to maintain an airgap (1175) therebetween. Additionally, the transducer (1172) includes aproximal end (1180) and a distal end (1182). The construction of theinner member (1174) can be in accordance with the description of theconstruction of the inner member (803)—disclosed above with reference toFIGS. 16A-16E. Thus, a further description of the inner member (1174) isnot believed to be necessary for one of ordinary skill in the art topractice the invention as disclosed herein.

[0346] As shown in FIG. 35, the transducer (1172) is supported relativeto the inner member (1174) by first and second end mounts (1184, 1186).The end mounts (1184, 1186) include at least a first metal surfaceportion (1188, 1190), respectively. The metal surface portions (1188,1190) are welded to the inner electrode (1178). Thus, a metal-to-metalconnection is formed between the end mount (1184) and the proximal end(1180) of the transducer (1172) and between the distal end (1182) andthe metal surface portion (1190) of the second end mount (1186). Themetal-to-metal contact between the inner electrode (1178) and the metalsurface portions (1188, 1190) can be formed through any conventionalmethods for welding, soldering, or the like.

[0347] The end mounts (1184, 1186) also include an inner surface (1192,1194), respectively. The inner surfaces (1192, 1194) are preferablysized to provide a close fit with an outer surface of the inner member(1174). The inner surfaces (1192, 1194) are bonded to the inner member(1174) with any appropriate adhesive or sealing substances. For example,the inner surfaces (1192, 1194) can be bonded to the inner member (1174)with silicone, loctite, epoxy, or any of a variety of adhesives.

[0348] In the illustrated embodiment, the end mounts (1184, 1186) are inthe form of metal bands. The bands can be formed out of any of a varietyof metals including, but without limitation, stainless steel andplatinum. However, as will be apparent from the description set forthbelow, the end mounts (1184, 1186) are not required to be solid metal.Rather, the end mounts (1184, 1186) may be formed from any materialhaving a metalized surface portion.

[0349] By mounting the transducer (1172) to the inner member (1174) witha plurality of end mounts which have at least a metal surface portion,e.g., (1188, 1190), the present transducer assembly (1170) will benefitfrom the high strength and highly temperature resistant metal-to-metalbonds created between the metal surface portions (1188, 1190) and theinner electrode (1178). Additionally, because the seal between the endmounts (1184, 1186) and the inner member (1174) are separated from thetransducer (1172), such seals are more protected from heat generated bythe transducer (1172). Thus, the present transducer assembly (1170)provides for enhanced life span and reliability of the seals provided atthe proximal and distal ends (1180, 1182) of the transducer (1172).

[0350]FIG. 36 illustrates a modification of the transducer mountingassembly (1170) illustrated in FIG. 35. In accordance with the presentmodification, a transducer assembly (1196) includes the transducer(1172) supported relative to the inner member (1174) by first and secondend mounts (1198,1200). In the illustrated embodiment, the end mounts(1198,1200) are formed of band members (1202,1204), each of which have ametal surface portion (1206,1208) connected to the inner electrode(1178). In the illustrated embodiment, the band members (1202,1204) aresupported by raised portions (1210,1212) provided on the inner member(1174).

[0351] In the illustrated embodiment, the raised portions (1210,1212)have an annular shape and are formed of a flexible material. Optionally,the raised portions (1210,1212) can be formed integrally with a layer ofsilicone (1214) formed around the inner member (1174). The proximal anddistal ends (1180,1182) of the transducer (1172) and the outer ends ofthe band members (1202,1204) are sealed with the raised portion(1210,1212) with epoxy fillets.

[0352] As noted above with respect to the embodiment illustrated in FIG.35, by welding or soldering, the inner electrode (1178) to the metalsurface portions (1206,1208) of the band members (1202,1204), thepresent modification benefits from the metal-to-metal seal providedbetween the metal surface portions (1206,1208) and the inner electrode(1178). Additionally, since the seal between the band members(1202,1204) and the raised portions (1210,1212) are spaced from thetransducer (1172), the seal therebetween is protected from heatgenerated by the transducer (1172) and thus suffers less deteriorationcaused by heat generated by the transducer (1172).

[0353]FIG. 37A illustrates a further modification of the embodimentillustrated in FIG. 35. As shown in FIG. 37A, a transducer assembly(1216) includes the transducer (1172) mounted to the inner member(1174). An annular support member (1218) is provided between the innerelectrode (1178) and the outer surface of the inner member (1174). Inthe present modification, the spacer member (1218) is a tubular-shapedmember formed of a rigid material such as, for example, but withoutlimitation, polyimide.

[0354] At proximal and distal ends (1220,1222) of the support member(1218), metal surface portions (1224,1226) are provided on an outersurface of the support member (1218). The metal surface portions(1224,1226) are welded or soldered to the inner electrode (1178).Additionally, loctite and/or silicone fillets can be provided over theproximal and distal ends (1180,1182) of the transducer (1172) as well asthe proximal and distal end (1220,1222) of the support member (1218),although such fillets are not shown.

[0355] In the illustrated embodiment, the inner electrode (1178) iswelded or soldered to the metal surface portions (1224,1226) only at theproximal and distal ends (1180,1182) of the transducer (1172). Theremaining outer surface portions of the support member (1218) and theinner electrode (1178) are not connected. Thus, although the supportmember (1218) has a substantially uniform thickness over its entirelength, the transducer assembly (1216) remains substantially air backed.

[0356] As noted above with respect to the transducer assembly (1170)illustrated in FIG. 35, the seal between the support member (1218) andthe inner member (1174) is spaced from the transducer (1172), and thusis protected from the damaging effects of heat generated by thetransducer (1172).

[0357]FIG. 37B illustrates a further modification of the embodimentillustrated in FIG. 37A. As shown in FIG. 37B, a transducer assembly(1228) includes the transducer (1172) supported relative to the innermember (1174) by support assembly (1230). In the illustrated embodiment,the support assembly (1230) is comprised of a pair of individual bandssimilar to the construction of the end mounts (1184,1186) illustrated inFIG. 35.

[0358] In the present modification, the support assembly (1230) isformed of a pair of plastic bands (1232,1234) having an outer metalsurface portion (1236,1238). In the illustrated embodiment, the plasticbands (1232,1234) are formed of polyimide. The outer metal surfaceportions (1236,1238) can be formed of any number of metals, for example,but without limitation, platinum, stainless steel, and nitenol. Theinner electrode (1178) can be fixed to the metal surface portions(1236,1238) in accordance with the description set forth above withrespect to FIG. 35. Additionally, the proximal and distal ends(1180,1182) of the transducer and bands (1232,1234) can be sealed withadhesives such as silicone, loctite, or other similar adhesives.

[0359]FIG. 38A illustrates a further modification of the embodimentillustrated in FIG. 35. As shown in FIG. 38A, a transducer assembly(1240) includes the transducer (1172) supported relative to the innermember (1174) so as to maintain the air gap (1175) between the innerelectrode (1178) and an outer surface (1242) of the inner member (1174),via a support assembly (1244). In the illustrated embodiment, thesupport assembly (1244) includes end mounts (1246,1248).

[0360] In the present modification, the end mounts (1246) are formed ofmetallic bands (1250,1252) which have inner ends (1254, 1256) and outerends (1258,1260). The metal bands (1250,1252) are soldered or welded tothe inner electrode (1178) at the inner ends (1254,1256), respectively.

[0361] The outer ends (1258,1260) of the metallic bands (1250,1252) aresealed to the outer surface (1242) of the inner member (1174) with asealant (1262,1264), respectively. In the illustrated embodiment, thesealant (1262,1264) can be any known adhesive, including, but withoutlimitation, silicone and loctite.

[0362] As noted above with respect to FIG. 35, by providing ametal-to-metal connection between the inner electrode (1178) and thebands (1250,1252), the seal generated by the weld or solder is greatlyenhanced due to the high strength and high temperature resistance ofsuch a seal. Additionally, since the outer ends (1258,1260) of the bands(1250,1252) are sealed to the outer surface (1242) of the inner member(1174), the sealants (1262,1264) are spaced from and thus protected fromheat generated by the transducer (1172). Thus, the air space (1175) isprovided with an enhanced fluid-tight seal.

[0363] As shown in FIG. 38A, the weld (1257) between the inner electrode(1178) and the inner ends (1254,1256) are spaced longitudinally from thesealant (1262,1264) such that the welds (1257) do not overlap with thesealants (1262,1264). Thus, the sealants (1262,1264) are further spacedfrom and thus protected from heat generated by the transducer (1172).

[0364] Additionally, in the illustrated embodiment, insulative fillets(1266,1268) are provided over the welds (1257) and the bands(1250,1252). As such, the inner and outer electrodes (1178,1176) areprevented from shorting when an ablation fluid is moved into contactwith the outer electrode (1176).

[0365] Additionally, as shown in FIG. 38A, an outer electrode lead(1270) is electrically connected to the outer electrode (1176) and aninner electrode lead (1272) is electrically coupled to the band (1250).Thus, by providing at least one band, e.g., band (1250) which issoldered, welded, or otherwise electrically connected with the innerelectrode (1178), the inner electrode electric lead wire (1272) can bemore easily connected to the inner electrode (1178) via conductionthrough the metal band (1250).

[0366] With reference to FIG. 38B, a modification of the connectionbetween the inner electrode (1178) and the metallic band (1252) isillustrated therein. As shown in FIG. 38B, the inner electrode (1178)can include an extension (1274) which extends around the distal orproximal end (1180,1182) of the electrode (1172) and along an annularend face (1276) of the electrode (1172).

[0367] By including an extension such as extension (1274) along theouter annular face (1276) of the electrode (1172), the connectionachieved by a fillet solder or weld (1257) is enhanced. In the presentmodification, an insulation material (1268) is distributed over theextension (1274), the weld (1257) and the metallic band (1252) so as toensure that current cannot be conducted between the extension (1274) andthe upper electrode (1176).

[0368] In a presently preferred embodiment, the extension (1274) extendsonly partially along the annular face (1276). However, it is conceivedthat the extension (1274) could extend completely over the annular face(1274), with a gap provided between an upper edge of the extension(1274) and the outer electrode (1176). It is also conceived that theinner electrode (1178) could be formed such that the extension (1274)extends onto the outer surface of the transducer (1172), and a gap issubsequently machined on the outer surface, so as to prevent the innerand outer electrodes (1176,1178) from shorting. In this mode, additionalinsulation may be required to prevent an ablation fluid from shortingthe electrodes (1176,1178).

[0369]FIGS. 39A and 39B illustrate further modification of theembodiment illustrated in FIG. 35. As shown in FIG. 39A, the bandmembers (1184,1186) are generally in the form of right circularcylinders. However, in the present modification, band members(1184,1186) can be in the form of truncated conical bands (1280). Forexample, as shown in FIG. 39B, a transducer assembly (1282) includes thetransducer (1172) supported relative to the inner member (1174) bysupport assembly (1284). In the present modification, the supportassembly (1284) comprises a pair of conical band members (1286,1288).The band member (1286,1288) include an outer narrowed end (1290,1292)and an inner enlarged end (1294,1296), respectively. Similarly to theembodiment illustrated in FIG. 35, the band members (1286,1288) eachinclude at least a metal surface portion (1298,1300) affixed to theinner electrode (1178) by welding, solder, or the like.

[0370] As shown in FIG. 39B, the outer narrowed ends (1290,1292) aresized so as to form a close fit with the outer surface (1242) of theinner member (1174). The outer narrow ends (1290,1292) are also sealedto the outer surface (1242) with silicone fillets (1302,1304).

[0371] Optionally, the outer surface (1242) of the inner member (1174)can include a coating of silicone prior to the installation of the bandmembers (1286,1288). Thus, after the band members (1286,1288) have beeninstalled over the silicone layer provided over the outer surface(1242), further silicone fillets (1302,1304) are provided over the bandmembers (1286,1288) and provide an enhanced seal between the outernarrow ends (1290,1292) and the inner member 1174.

[0372] As shown in FIG. 39B, the silicone layer 1306 may be applied tothe entire outer surface (1242) of the inner member (1174). However, anyportion of the silicone layer (1306) positioned within the transducer(1172) is optional.

[0373] As noted above with respect to FIGS. 35-38B, by providing ametal-to-metal bond between the inner electrode (1178) and the innerends of the band members (1286,1288), the inner electrode is reliablyconnected to the band members (1286,1288) with a high strength and hightemperature-resistant connection. Additionally, the seal between thenarrowed ends (1290,1292) of the band members (1286,1288) is furtherspaced from the transducer (1172) and thus protected from heat generatedby the transducer (1172).

[0374]FIG. 40 illustrates a further modification of the embodimentillustrated in FIG. 35. As shown in FIG. 40, a transducer assembly(1308) includes the transducer (1172) supported relative to the innermember (1174) so as to maintain the air gap (1175) between the innerelectrode (1178) and the outer surface (1242) of the inner member(1174), via a support assembly (1310). In the illustrated embodiment,the support assembly (1310) comprised of a pair of trumpet-shapedmembers (1312,1314).

[0375] In contrast to the modification illustrated in FIG. 39, thetrumpet-shaped members (1312,1314) include inner narrowed ends(1316,1318) and enlarged outer ends (1320,1322). In the illustratedembodiment, the inner ends (1316,1318) are bonded to the outer surface(1242) of the inner member (1174) with loctite. The remaining inner andouter surfaces of the trumpet-shaped members (1312,1314) are coveredwith epoxy fillets (1324,1326), respectively. Optionally, thetrumpet-shaped members (1312,1314) may include metal surface portions(1328,1330) which are welded or soldered to the inner electrode (1178).

[0376]FIG. 41 illustrates yet another modification of the embodimentillustrated in FIG. 35. As shown in FIG. 41, a transducer assembly(1328) includes the transducer (1172) supported relative to the outersurface (1242) of the inner member (1174) by a support assembly (1330).In the illustrated embodiment, the support assembly (1330) includes apair of band members (1332,1334). The band members (1332,1334) includeat least a metal surface portion (1336,1338) on the inner ends thereof,respectively.

[0377] The metal surface portions (1336,1338) are soldered, welded, orconnected by any other method for producing a metal-to-metal orelectrical coupling connection between the band members (1332,1334) andthe outer electrode (1176) of the transducer (1172).

[0378] As shown in FIG. 41, the band members (1332, 1334) are adhered tothe outer surface (1242) with an adhesive or insulating material (1340).The material (1340) can be any appropriate insulative or adhesivematerial such as, for example, but without limitation, silicone, epoxy,and/or loctite. The transducer (1172) is connected to a power supply,such as the power supply (840) illustrated in FIG. 16D by an outerelectrode lead (1342) and an inner electrode lead (1344). As shown inFIG. 41, the outer electrode lead (1342) is connected to the metallicband member (1332). Additionally, the inner electrode lead (1334) isconnected to the inner electrode (1178) directly.

[0379] In the illustrated embodiment, since the band members (1332,1334)are connected to the outer electrode (1176), there is no need toinsulate the band members (1332,1334) from the outer electrode (1176).However, as noted above with respect to FIG. 35, the seal between theband members (1332,1334) and the outer surface (1242) of the innermember (1174) is protected by the spacing and separation from thetransducer (1172). It is also conceived that the assembly (1328) caninclude additional band members (not shown) extending from the innerelectrode (1178) and outwardly from the transducer (1172). In this mode,connection of the electrodes (1176,1178) with lead wires is easier.

[0380]FIGS. 42A and 42B illustrate another modification of theembodiment illustrated in FIG. 35. As shown in FIG. 42A, a transducerassembly (1346) includes the transducer (1172) supported relative to theouter surface (1242) of the inner member (1174) via a mounting assembly(1348). In the illustrated embodiment, the mounting assembly (1348) iscomprised of a braided metal tubular member (1350) (shown in section)arranged between the inner electrode (1178) and the outer surface (1242)of the inner member (1174).

[0381] The inner electrode (1178) is soldered or welded to the tubularbraided member (1350) at the proximal and distal ends (1180,1182) of thetransducer (1172). In the illustrated embodiment, the tubular, braidedmember (1350) extends continuously between the proximal and distal ends(1180,1182) of the transducer (1172). Since the tubular member (1350) isformed of a braided metal, the air gap (1175) is maintained despite thepresence of the braided tubular member (1350) in the air gap (1175).

[0382] As shown in FIG. 42, an insulative and/or adhesive material(1352) is disposed over the welded portions (1351) in the portion of thebraided tubular member (1350) extending outwardly therefrom, therebysealing the air space (1175). Although not shown, further insulation canbe provided over any portion of the tubular braided member (1350) thatmay be exposed to fluid during a tissue ablation process.

[0383]FIG. 42B illustrates a modification of the modificationillustrated in FIG. 42A. As shown in FIG. 42B, the portion of thetubular braided member (1350) extending within the transducer (1172) hasbeen removed, thus enhancing the air backing provided by the air gap(1175).

[0384]FIGS. 43A and 43B illustrate yet another modification of theembodiment illustrated in FIG. 35. As shown in FIG. 43, acircumferential ablation device assembly (1360) includes an elongatebody (1362) defining a multilumen catheter body. The elongate body(1362) includes a proximal end (1364) and a distal end (1366). Theassembly (1360) also includes an expandable balloon (1368) located alongthe distal end portion (1366) of the elongate body (1362) and around thecircumferential ultrasound transducer (1172).

[0385] As noted above, the transducer (1172) forms a circumferentialablation member which is acoustically coupled to the expandable balloon(1368). The multilumen shaft (1364) can include a variety of lumensincluding, for example, but without limitation, a guidewire lumen, aninflation lumen, an electrical lead lumen, and a cooling fluid lumen.However, FIG. 43 only illustrates the guidewire lumen (1370) and theinflation lumen (1372).

[0386] The construction of the expandable balloon (1368) can be inaccordance with the description of the expandable balloon (820)disclosed above with reference to FIGS. 16A-16E. Thus, furtherdescription of the expandable balloon (1368) is not necessary for one ofordinary skill in the art to practice the invention as disclosed herein.

[0387] Similarly, the construction of the multilumen shaft (1364) can bemade in accordance with the description of the elongate body (802)disclosed above with reference to FIGS. 16A-16D. Thus, for thedescription of the multi-lumen shaft (1364) is not necessary for one ofordinary skill in the art to practice the invention as disclosed herein.

[0388] As shown in FIG. 43A, the inner member (1174) extends from theguidewire lumen (1370) through the interior of the expandable balloon(1368). In the present modification, the assembly (1360) includes asilicone lamination (1374) extending over the outer surface (1242) ofthe inner member (1174).

[0389] An optional method for forming the lamination of silicone (1374)is to dip the inner member (1174) into a silicone dispersion using aprocess similar to that used to make the expandable balloon (1368) ofsilicone. Another method can include taking a silicone tube having aninner diameter smaller than the outer diameter of the inner member(1174), applying heptane to the silicone tube to cause it to swell,sliding the swollen silicone tube over the inner member (1174), thenallowing the silicone tube to shrink onto the inner member (1174) as theheptane evaporates. A further alternative method for forming thesilicone adhesive includes spreading a silicone adhesive over the lengthof the inner member (1174) and then allowing it to cure.

[0390] Optionally, a metal coil or braid could be incorporated into thesilicone lamination to prevent the silicone layer (1374) fromdelaminating from the outer surface (1242). As noted above with respectto FIGS. 42A and 42B, such use of a metal coil or braid can furtherprovide peaks and valleys which aid in ensuring sufficient air backingfor the transducer (1172).

[0391] As shown in FIG. 43B, the transducer (1172) is supported relativeto the inner member (1174) by a support assembly (1376). In theillustrated embodiment, the support assembly (1376) includes twometallic bands (1378, 1380) which can be constructed in accordance withthe metallic bands (1250, 1252) illustrated in FIG. 38A. Additionally,the bands (1378, 1380) can be connected to the inner electrode (1178) inaccordance with the disclosure set forth above with respect to the welds(1257) set forth above with reference to FIG. 38A. Additionally, theinner and outer electrodes (1178, 1176) can be attached to the innerelectrode lead (1272) and the outer electrode lead (1270) as disclosedabove with reference to FIG. 38.

[0392] In the illustrated embodiment, the outer ends (1258, 1260) of thebands (1378, 1380) are sealed to the silicone lamination (1374) withadditional fillets of silicone (1382, 1384). By mounting the bandmembers (1378, 1380) to the silicone lamination (1374) as such,assembling the assembly (1360) is made easier. By having the siliconelamination present completely under the transducer and extending for asubstantial length from either side of the transducer, the potential forfluid ingress under the transducer is virtually eliminated. Any fluidthat seeps between the silicone and the inner member is more likely tostay under the silicone material and be prevented from seeping into theair space (1175) under the transducer (1172).

[0393] As noted above with respect to FIG. 35, the soldered or weldedconnections between the bands (1378, 1380) and the inner electrode(1178) provide a high strength and highly temperature resistant seal forpreventing fluid from seeping into the air space (1175) from theinterior of the expandable balloon (1168).

[0394]FIG. 44 illustrates a modification of the assembly (1360)illustrated in FIG. 43A. As shown in FIG. 44, a circumferential ablationdevice assembly (1386) includes an elongate body (1388) including aproximal end (not shown) and a distal end (1390). The assembly (1386)also includes an expandable balloon (1392) and an ablation elementassembly (1394). The construction of the elongate body (1388) can be inaccordance with the description of the elongate body (802) set forthabove with reference to FIGS. 16A-16D. The construction of theexpandable balloon (1392) can be made in accordance with the descriptionof the expandable balloon (820) set forth above with reference to FIGS.16A-16D. Thus, a further description of the elongate body (1388) and theexpandable balloon (1392) is not necessary for one of ordinary skill inthe art to practice the invention as disclosed herein.

[0395] As shown in FIG. 44, the ablation element assembly (1394)includes the circumferential ultrasound transducer (1172) having aproximal end (1180) and a distal end (1182). Additionally, thetransducer (1172) includes an outer electrode (1176) and an innerelectrode (1178).

[0396] The ablation element assembly (1394) also includes an innermember assembly (1396) having an inner surface (1397) and extending fromthe elongate member (1388) and along the guidewire lumen (1370). Asshown in FIG. 44, the inner member assembly (1394) includes a proximalmounting end (1398), a transducer support portion (1400) and a distalend (1402). The proximal mounting portion (1398) is sized to provide atight fit with an inner diameter of the guidewire lumen (1370), therebyfixing the inner member assembly (1396) to the elongate body (1388). Thedistal portion (1402) of the inner member assembly (1396) extendsdistally from the transducer support portion (1400) and provides amounting area for the distal end of the expandable balloon (1392).

[0397] In the illustrated embodiment, the elongate body (1388) ispreferably made from a PEBAX material. The distal end (1402) of theinner member assembly (1396) includes a tubular extension (1404) whichis also preferably made from a PEBAX material. The PEBAX material usedin the tubular extension (1404) should be softer than the PEBAX materialused to construct the elongate member (1388) such that the inner memberprovides a soft tip. Further, a silicone fillet portion (1406) isprovided on the extreme distal end of the expandable balloon (1392) toensure smooth insertion of the distal end of the assembly (1386) into abody structure.

[0398] The transducer support portion (1400) includes a main bodyportion (1408) extending between the proximal and distal ends (1180,1182) of the transducer (1172). At the proximal and distal ends (1180,1182), the body portion includes raised portions (1410, 1412) whichdefine an air gap (1175) between the transducer (1172) and the main bodyportion (1408). The entire inner member assembly (1396) is preferablyformed from a metal, such as, for example, but without limitation,stainless steel, platinum, nitinol, and the like. In the illustratedembodiment, the inner electrode (1178) is soldered or welded to theraised portions (1410, 1412). Thus, the inner electrode lead (1272) canbe connected directly to the inner member (1396).

[0399] In order to insulate the outer surface of the metallic innermember assembly (1396), insulative fillets (1414, 1416) are providedover the ends of the transducer support portion (1400) which wouldotherwise be exposed to the interior of the expandable balloon (1392).

[0400] Optionally, the main body (1408) of the inner member assembly(1396) can be formed from a hypodermic-sized metal tube, with the raisedportions (1410, 1412) machined onto the outer surface. Alternatively,the raised portions (1410, 1412) can be constructed of separate annularpieces bonded to the outer surface of the body (1408). Preferably, theinner surface (1397) of the inner member assembly is coated with aninsulating material, such as, for example, but without limitation,Teflon, polyimide, or the like.

[0401] By forming the inner member assembly (1396) from a metalmaterial, the entire distal end portion (1390) of the assembly (1386) isprovided with additional rigidity. The additional rigidity is useful inpreventing the damaging effects of bending around the proximal anddistal ends (1180, 1182) of the transducer (1172) which can damage theseals between the transducer and the inner member (1396).

[0402] Common to a number of modes described above, an outer cover orlayer has been removed from the transducer and an improved seal has beenprovided between the transducer and the supporting structure of thedelivery member (e.g., the catheter shaft). It has been observed thatwith no cover layer, with the particular transducer described above, andwith the transducer driven at the power levels described herein, theultrasound transducer can be used to form sufficient tissue ablation ata location where a pulmonary vein extends from an atrium so as to forman effective conduction block. This result is achieved even though thetransducer is supported on the delivery member by a non-elastomericstructure (e.g., by a rigid structure such as those described above inconnection with FIGS. 30A-44).

[0403] While particular detailed description has been herein providedfor particular embodiments and variations according to the presentinvention, it is further understood that various modifications andimprovements may be made by one of ordinary skill according to thisdisclosure and without departing from the broad scope of the invention.

[0404] It is further contemplated that the embodiments shown anddescribed herein may be combined, assembled together, or whereappropriate substituted for the various features and embodiments whichare disclosed in the following co-pending provisional andnon-provisional U.S. patent applications: the co-pending non-provisionalU.S. patent application for “FEEDBACK APPARATUS AND METHOD FOR ABLATIONAT PULMONARY VEIN OSTIUM”, filed on the same day as this Application,and claiming priority to Provisional U.S. Patent Application No.60/122,571, filed on Mar. 2, 1999; the co-pending non-provisional U.S.patent application for “CIRCUMFERENTIAL ABLATION DEVICE ASSEMBLY ANDMETHODS OF USE AND MANUFACTURE PROVIDING AN ABLATIVE CIRCUMFERENTIALBAND ALONG AN EXPANDABLE MEMBER”, filed on the same day as thisApplication, and which claims priority to Provisional U.S. ApplicationNo. 60/125,509, filed Mar. 19, 1999; the co-pending non-provisional U.S.patent application for “CIRCUMFERENTIAL ABLATION DEVICE ASSEMBLY ANDMETHODS OF USE AND MANUFACTURE PROVIDING AN ABLATIVE CIRCUMFERENTIALBAND ALONG AN EXPANDABLE MEMBER”, filed on the same day as thisApplication, and which claims priority to Provisional U.S. PatentApplication No. 60/125,928, filed Mar. 23, 1999; co-pending ProvisionalU.S. Patent Application No. 60/133,610 for “BALLOON ANCHOR WIRE”, filedMay 11, 1999; the co-pending non-provisional U.S. patent application for“TISSUE ABLATION DEVICE ASSEMBLY AND METHOD FOR ELECTRICALLY ISOLATING APULMONARY VEIN OSTIUM FROM A POSTERIOR LEFT ATRIAL WALL”, filed on thesame day as this Application, and which claims priority to ProvisionalU.S. Patent Application No. 60/133,677, filed May 11, 1999; andco-pending Provisional U.S. Patent Application Ser. No. 60/133,807 for“CATHETER POSITIONING SYSTEM”, filed May 11, 1999. The disclosures ofthese references are herein incorporated in their entirety by referencethereto.

[0405] In addition, a circumferential ablation device assemblyconstructed with a mounted ultrasound ablation element according to thepresent invention may be used in combination with other linear ablationassemblies and methods, and various related components or steps of suchassemblies or methods, respectively, in order to form a circumferentialconduction block adjunctively to the formation of long linear lesions,such as in a less-invasive “maze”-type procedure. Examples of suchassemblies and methods related to linear lesion formation and which arecontemplated in combination with the presently disclosed embodiments areshown and described in the following additional co-pending U.S. patentapplications: U.S. Ser. No. 08/853,861 entitled “TISSUE ABLATION DEVICEAND METHOD OF USE” filed by Michael Lesh, M.D. on May 9, 1997, now U.S.Pat. No. 5,971,983, issued Oct. 26, 1999 ; U.S. Ser. No. 09/260,316 for“TISSUE ABLATION SYSTEM AND METHOD FOR FORMING LONG LINEAR LESION” toLangberg et al., filed May 1, 1999; and U.S. Ser. No. 09/073,907 for“TISSUE ABLATION DEVICE WITH FLUID IRRIGATED ELECTRODE”, to Alan Schaeret al., filed May 6, 1998. The disclosures of these references areherein incorporated in their entirety by reference thereto.

[0406] In addition, one of ordinary skill may make other obvious orinsubstantial modifications or improvements to the specific embodimentsherein shown and described based upon this disclosure without departingfrom the scope of the invention as defined by the claims which follow.

What is claimed is:
 1. An ultrasound ablation apparatus comprising: anelongate catheter body having proximal and distal end portions, an outerwall and an outer diameter; a cylindrical ultrasound transducercoaxially disposed over said catheter body, said ultrasound transducerhaving proximal and distal end portions, an inner wall and an innerdiameter which is greater than the outer diameter of said catheter body,such that an air gap is provided in a radial separation between theinner wall of said ultrasound transducer and said catheter body; and asupport structure for suspending said ultrasound transducer in asubstantially fixed coaxial position relative to said catheter body,wherein said support structure contacts the outer wall of said catheterbody at locations proximal and distal to the proximal and distal endportions of said ultrasound transducer, respectively, and wherein saidsupport structure holds said ultrasound transducer without contactingthe inner wall of said ultrasound transducer, thereby maintaining saidradial separation while reducing acoustic damping caused by said supportstructure.
 2. The ultrasound ablation apparatus of claim 1, wherein saidultrasound transducer is shaped to ablate a circumferential region oftissue.
 3. The ultrasound ablation apparatus of claim 1, wherein saidultrasound transducer comprises at least one transmissive panel.
 4. Theultrasound ablation apparatus of claim 1, wherein at least a substantialportion of said radial separation is sealed by said support structure toprevent external fluids from entering said radial separation.
 5. Theultrasound ablation apparatus of claim 4, wherein a gas is sealed withinsaid radial separation.
 6. The ultrasound ablation apparatus of claim 4,wherein a liquid is sealed within said radial separation.
 7. Theultrasound ablation apparatus of claim 1, further comprising first andsecond flanges extending axially from the proximal and distal endportions of said ultrasound transducer, respectively, said supportstructure being coupled to said first and second flanges.
 8. Theultrasound ablation apparatus of claim 7, wherein said support structurefurther comprises first and second elastomeric O-rings disposed on saidcatheter body such that said first and second O-rings engage said firstand second flanges.
 9. The ultrasound ablation apparatus of claim 7,wherein said support structure further comprises first and secondsleeves disposed on said catheter body and fitted over said first andsecond flanges, to secure said ultrasound transducer relative to saidcatheter body.
 10. The ultrasound ablation apparatus of claim 7, whereinsaid support structure further comprises first and second splinesdisposed on said catheter body such that said first and second splinesengage said first and second flanges.
 11. The ultrasound ablationapparatus of claim 7, wherein said support structure further comprisesfirst and second annular members disposed along said catheter body suchthat said first and second annular members engage said first and secondflanges.
 12. The ultrasound ablation apparatus of claim 1, wherein saidsupport structure further comprises first and second annular membersdisposed on said catheter body, said first and second annular membersfrictionally engaging the proximal and distal end portions of saidultrasound transducer.
 13. The ultrasound ablation apparatus of claim 1,wherein said support structure further comprises a shrink-wrap coverlayer disposed around said ultrasound transducer.
 14. The ultrasoundablation apparatus of claim 1, further comprising an expandable memberadapted to engage a circumferential region of tissue, said ultrasoundtransducer being located inside said expandable member and acousticallycoupled to said expandable member.
 15. The ultrasound ablation apparatusof claim 14, wherein said expandable member is an inflatable balloon.16. The ultrasound ablation apparatus of claim 14, wherein a coolingchamber is provided between said ultrasound transducer and saidexpandable member, said cooling chamber being adapted to allow a coolingfluid to flow over said ultrasound transducer.
 17. The ultrasoundablation apparatus of claim 16, further comprising a source ofpressurized cooling fluid and a cooling fluid lumen in said catheterbody, said lumen having a distal port opening into said cooling chamber.18. The ultrasound ablation apparatus of claim 14, further comprising athermocouple for monitoring temperature along at least a portion of saidcircumferential region of tissue engaged by said expandable member. 19.The ultrasound ablation apparatus of claim 1, further comprising atleast one electrical lead coupled to said ultrasound transducer.
 20. Theultrasound ablation apparatus of claim 1, further comprising filletslocated proximal and distal to the proximal and distal end portions ofsaid ultrasound transducer for sealing said radial separation from entryof external fluids and providing a smooth surface for insertion of saidultrasound ablation apparatus into a body structure.
 21. The ultrasoundablation apparatus of claim 1 further comprising a guidewire lumenextending through at least a portion of said catheter body for slidablyengaging a guidewire.
 22. An ultrasound ablation apparatus, comprising:an elongate catheter body; an cylindrical ultrasound transducer havingfirst and second ends and inner and outer surfaces, said ultrasoundtransducer being mounted coaxially on said catheter body such that aradial separation is provided between said ultrasound transducer andsaid catheter body for mechanically isolating said ultrasound transducerfrom said catheter body; and a support structure coupled to saidultrasound transducer and said catheter body to maintain at least aregion of said radial separation for reducing acoustic damping caused bysaid support structure.
 23. The ultrasound ablation apparatus of claim22, wherein said support structure further comprises first and secondannular members disposed along said catheter body such that said firstand second annular members engage said inner surface of said ultrasoundtransducer.
 24. The ultrasound ablation apparatus of claim 23, whereinsaid first and second annular end members have a metallic exteriorsurface adapted to engage said inner surface of said ultrasoundtransducer.
 25. The ultrasound ablation apparatus of claim 23, furthercomprising an annular intermediate portion disposed on said catheterbody and located between said first and second annular members.
 26. Theultrasound ablation apparatus of claim 22, wherein said supportstructure further comprises a substantially tubular member disposed oversaid catheter body, said tubular member having proximal and distal endregions and an intermediate region, said proximal and distal end regionsbeing formed with a larger diameter than said intermediate region, saidultrasound transducer being disposed over said intermediate region suchthat it is axially contained by said proximal and distal end regions.27. The ultrasound ablation apparatus of claim 22, wherein said supportstructure further comprises at least one mandrel extending axially alongsaid catheter body, said at least one mandrel engaging said catheterbody and said inner surface of said ultrasound transducer.
 28. Theultrasound ablation apparatus of claim 26, wherein said at least onemandrel further comprises a polyimide tube.
 29. The ultrasound ablationapparatus of claim 27, wherein said at least one mandrel furthercomprises a plurality of polyimide tubes positioned substantiallyuniformly around said catheter body within said radial separation. 30.The ultrasound ablation apparatus of claim 22, wherein said supportstructure further comprises a braided metal tubular member disposedaround said catheter body such that said radial separation is maintainedtherebetween, said ultrasound transducer being mounted coaxially oversaid braided tubular member.
 31. The ultrasound ablation apparatus ofclaim 22, wherein said support structure further comprises two braidedmetal tubular members disposed around said catheter body with an axialgap between said braided metal tubular members, said first and secondends of said ultrasound transducer being mounted to said braided tubularmembers thereby bridging said axial gap.
 32. The ultrasound ablationapparatus of claim 22, wherein said support structure further comprisestwo truncated conical members each having a first end with a largediameter and a second end with a small diameter, said conical membersbeing disposed over said catheter body such that said first ends faceinward and said second ends face outward, said inner surface of saidultrasound transducer being engaged by said first ends of said conicalmembers.
 33. The ultrasound ablation apparatus of claim 22, wherein saidsupport structure comprises an expandable member disposed over saidcatheter body and having an outer surface, wherein the inner surface ofsaid ultrasound transducer is coaxially engaged by the outer surface ofsaid expandable member.
 34. A method for treating arrythmia using anultrasound ablation apparatus comprising: providing an elongate catheterbody having a cylindrical ultrasound transducer coaxially disposed oversaid catheter body and a support structure for suspending saidultrasound transducer in a substantially fixed coaxial position relativeto said catheter body wherein said support structure contacts an outerwall of said catheter body at locations proximal and distal to saidultrasound transducer for maintaining a radial separation therebetweento reduce acoustic damping caused by said support structure; advancingsaid ultrasound transducer into a location where a pulmonary veinextends from an atrium; and supplying energy to said ultrasoundtransducer for acoustically coupling to a circumferential region oftissue at said location to form a circumferential conduction block.